Insulating microwave interactive packaging

ABSTRACT

The combination of insulating material with microwave interactive food packaging for enhanced cooking properties is disclosed. An insulating microwave packaging material ( 200 ) and a method of making the same are also disclosed. In one embodiment, the insulating microwave packaging material ( 200 ) is formed by bonding a microwave interactive material substrate ( 205 ) that creates sensible heat upon exposure to microwave energy to a second substrate ( 210 ) along bond lines ( 212 ) arranged in a pattern to form closed cells ( 214 ). Upon impingement of the insulating microwave packaging material ( 200 ) by microwave energy in a microwave oven, the closed cells ( 214 ) expand to form insulating pockets ( 216 ). One side of the insulating pocket ( 216 ) bulges and lofts above the opposite side. When a food product is situated on the insulating microwave packaging material ( 200 ), the insulating pockets ( 216 ) insulate the food product from the microwave oven environment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/314,851, filed Dec. 21, 2005, which is a continuation ofU.S. application Ser. No. 10/501,003, filed Mar. 7, 2005, now U.S. Pat.No. 7,019,271, issued Mar. 28, 2006, which is a national stage entryunder 35 U.S.C. §363 of PCT/US03/03779, filed Feb. 7, 2003, which claimspriority under 35 U.S.C. §119(e) to U.S. Provisional Application No.60/355,149, filed Feb. 8, 2002, each of which is hereby incorporated byreference in its entirety as though fully set forth herein.

TECHNICAL FIELD

This invention relates generally to the field of microwave packaging forfood products and more specifically to the insulation of microwavepackaging materials, including microwave interactive packaging material.

BACKGROUND

Many combinations of materials of different character have been combinedin microwave packaging to influence the cooking effect of the microwaveenergy on food products. These microwave packaging materials may beeither microwave transparent, for example, paper, paperboard, or manyplastics, or they may be microwave interactive, for example, metal foilsor thin metal deposits. Microwave transparent materials generallyprovide, for example, food product support, packaging form, insulation,and vapor barrier functions in packaging. Microwave interactivematerials generally provide, for example, enhanced surface heating,microwave shielding, enhanced microwave transmission, and energydistribution functions in packaging. Microwave packaging is generallycreated and configured for a particular food product or type of foodproduct using materials chosen to best exploit the cooking ability of amicrowave oven with respect to that food product.

For example, a microwave package design primarily for heating cornkernels to create popcorn is disclosed in U.S. Pat. No. 4,943,456 issuedto Pollart et al. (the '456 patent). The '456 patent describes a packageconstructed of an inner bag of polyester and an outer bag of paper. Amicrowave heating element is printed on either the inner surface of theouter bag or the outer surface of the inner bag, such that the heatingelement resides between the two bags. The heater element may be a solidarea or patterned, as in a grid. The outer surface of the inner bag andthe inner surface of the outer bag are laminated together. When the areaof the heater element is bonded to the opposing bag by fully laminatingthe bags together, the outer paper bag scorches or ignites duringmicrowave heating. By laminating the inner and outer bags together inthe area of the heater element using only a pattern of adhesive betweenthe bags (e.g., a dotted or grid adhesive pattern) the outer paper bagdoes not scorch during cooking.

In another example of microwave packaging design disclosed in U.S. Pat.No. 5,338,921 issued to Maheux et al. (the '921 patent), an improvementwas made to the use of metallized plastic film in surface heating,browning, and crisping of food products. It was found that unevenheating of the metallized film occurred when the film was completelylaminated to a stiff substrate backing. The '921 patent describessealing a sheet of the metallized film to the substrate only at theperiphery of the sheet, and further ensuring that the major area of thesheet hangs loose from the substrate such that it traps a large airpocket between the sheet and the substrate. In this manner, convectioncurrents in the air pocket are allowed to form and thus distribute theheat generated by the metallized film more evenly across the entiresurface of the metallized film sheet.

While improvements to the use of susceptor technology (the “heater” and“metallized film” discussed in the '456 patent and '921 patent,respectively) have been made as discussed above, the microwave packagingdesigns may still not achieve optimal performance of the susceptors. Forexample, with respect to the popcorn bag of the '456 patent, thesusceptor area is generally placed against the bottom surface of themicrowave oven during cooking so the popcorn kernels are situatedagainst the susceptor to receive the maximum possible heat transfer. Inthis configuration, the base of the microwave oven is also adjacent tothe susceptor. Much of the heat generated by the susceptor is thereforetransferred to the microwave oven surface (e.g., the glass turntable orfloor) and not to the popcorn kernels. The microwave oven environment isactually a large heat sink, impacting the efficiency of the ability ofthe susceptor to heat the food. The cavity of air within the microwaveoven is also constantly ventilated by a fan and creates a cooling effectwhile the microwave oven is in operation.

In the design disclosed in the '921 patent, the placement of thesusceptor material is in the top panel of the packaging. In this case,the susceptor is generally separated from the food product to be cookedby a gap between the top of the food in the package and the top of thepackage where the susceptor is placed. Thus the ability of the susceptorto heat the food is diminished because the susceptor is not in contactwith or very close to the surface of the food product. In fact, the airgap between the food and susceptor actually acts as an insulator andprevents the maximum possible heating of the food product by thesusceptor from occurring. In some situations, even if the susceptormaterial is originally against the food product when initially packaged,the food may actually shrink or change shape during cooking, forexample, if originally frozen, and the susceptor material loses contactwith the food product, impacting the ability of the susceptor to brownand crisp the food product.

The information included in this Background section of thespecification, including any references cited herein and any descriptionor discussion thereof, is included for technical reference purposes onlyand is not to be regarded as essential subject matter upon which theclaims of the present application depend for support, by which the scopeof the invention is to be bound, or upon which this application dependsfor adequate disclosure of the invention.

SUMMARY

The present invention enhances the cooking ability of microwaveinteractive materials in microwave packaging and provides additionalconsumer benefits through the addition of insulating materials to theconfiguration of microwave packaging. Particularly, by insulating aroundsusceptor material and retaining heat generated by the susceptor,increased browning and crisping, as well as moisture retention, areachieved. Several unique new designs for microwave packaging materialsinvolving the combination of microwave transparent and microwaveinteractive materials that achieve several new and beneficial resultsare disclosed. In one aspect of the invention, the disclosed microwavepackaging provides greater surface heating for a food product andinsulation from the effects of the heat sinks found in the microwaveoven environment. In another aspect, insulation surrounding microwaveinteractive packaging provides consumer protection and convenience asadded benefits.

An insulating microwave packaging material and a method of making thesame is disclosed. The insulating microwave packaging material is formedby adhering a microwave interactive substrate that creates sensible heatto a second substrate in a pattern bond creating closed cells. Uponimpingement of the insulating microwave packaging material by microwaveenergy in a microwave oven, moisture trapped in either the firstmicrowave interactive substrate or the second substrate heats, expands,and escapes, creating pressure that expands the closed cells to formvapor pockets. The microwave interactive substrate bulges under thevapor pressure while the second substrate contracts to enhance thebulging effect on the cell and create the pocket.

In one particular embodiment the microwave interactive substrate may beformed by creating a metallized polyester film, i.e., a susceptor film(generally by depositing a thin layer of aluminum on a sheet ofpolyester). This metallized polyester film is then bonded to a papersubstrate to create a susceptor. The susceptor is then bonded to asecond polyester film, preferably biaxially-oriented, clear polyester,along bond lines arranged in a pattern to form closed cells. The closedcells are substantially vapor impermeable.

Simultaneously, the sensible heat generated by the susceptor heats andsoftens the polyester film of the susceptor, decreasing the resistanceof the susceptor to the expansion of the moisture and the formation ofthe vapor pocket. Additionally, the second polyester film, which is notmetallized, also heats because of its proximity to the susceptor.Because it is biaxially-oriented, the second polyester film contractsalong its length and width, attempting to return to its original formbefore stretching. The second polyester layer remains substantially flatrather than lofting. Yielding to the pressure of the expanding watervapor, in each cell the softened susceptor layer bulges opposite thesecond polyester film layer forming pillow-like pockets on the susceptorside of the microwave packaging material. The contraction of the secondpolyester layer works in conjunction with the bulging of the susceptorto enhance the loft of the pillow-like side of the cells.

The loft obtained by the vapor expansion in the cells and the polyesterfilm contraction is generally at least an order of magnitude greaterthan the original separation between the susceptor and the second sheetof polyester film, and in some cases has been observed to be 30 timesmore than the original thickness of the microwave packaging material.When a food product is situated on the pillow-like side of theinsulating microwave packaging material, the vapor pockets insulate thefood product from the microwave oven to reduce heat transfer between thefood product and the microwave oven environment, e.g., the air in theoven cavity and the oven floor or turntable surface. The amount of loftmay be varied by choosing paper with higher or lower moisture content orotherwise introducing and trapping moisture in the cells during themanufacturing process.

The pattern of bond lines forming the closed cells of the insulatingmicrowave packaging material generally define an array of shapes. Suchshapes may be, for example, circles, ovals, other curvilinear shapes,preferably symmetrical, triangles, squares, rectangles, hexagons, andother polygons, including right polygons and equilateral polygons. Theshapes in the array are preferably nested with adjacent shapes in thearray in a tile-like pattern. In an alternative embodiment, the shapesmay be elongate and arranged in parallel with the long sides of eachadjacent shape next to each other. The pattern of bond lines may beformed by the application of adhesive on the paper substrate side of thesusceptor to bond the susceptor with the second polyester film. In oneembodiment, the susceptor film may be selectively deactivated in thesame pattern as the adhesive bond lines. By deactivating the susceptorfilm in these areas, the adhesive bond may be stronger because theadhesive is not directly subjected to the extreme heat generated by thesusceptor film. In another embodiment, by selectively deactivating thesusceptor film in coordination with the bond patterns, aconsumer-friendly product is created as the bond pattern areas arecooler to the touch than other areas of the packaging material. Therebythe packaging material may be easily handled by the user after microwaveheating.

In one embodiment of the invention, the insulating microwave packagingmaterial is used within a carton. A first sheet of the insulatingmicrowave packaging material is affixed to the top surface of the cartonin a manner allowing the first sheet to contract in at least on of the Xand Y directions upon microwave heating. Similarly, a second sheet ofinsulating microwave packaging material is affixed to the bottom surfacein a manner allowing the second sheet to likewise contract in at leaston of the X and Y directions upon exposure microwave energy. The sheetsmay be cut along their perimeters to form slits that augment the abilityof the sheets to contract in the X and Y directions.

In one embodiment, a sheet of the insulating microwave packagingmaterial is folded over and the two opposing edges brought into contactare bonded together, for example, with adhesive or by heat sealing theedges. The microwave packaging material thereby forms a sleeve forsurrounding the food product. The susceptor layer generally forms theinterior surface of the sleeve. When exposed to microwave energy, thecells expand inward toward the food product ensuring the susceptorcontacts all the surfaces of the food product. At the same time, thatportion of the microwave packaging material resting on the coolingplatform in the microwave oven provides improved insulation from thefloor or turntable of the microwave oven by the vapor in the cells.

In a another embodiment of the invention, two sheets of the insulatingmicrowave packaging material are placed back to back and bonded togetherat several points, generally around the perimeters of the sheets. Inthis embodiment, the second clear polyester film sides of the sheets maybe together, while the susceptor sides of the sheets face outward. Byonly bonding the sheets together at a few places, for example, on thecorners if the sheets are square or rectangular, there is still freedomof movement for contraction of the second clear polyester film layers inthe X-Y dimensions upon heating. In this embodiment, the sheets furtherdeform on a macro scale to form opposing convex canopies with an airspace in between, providing additional insulation from the microwaveoven. Further, the combination of two sheets helps ensure the cellexpansion of the top sheet, for example, when the food product to beheated is frozen. In such an instance, the susceptor of the bottom sheethelps heat the top sheet to ensure it reaches a high enough temperatureearly in the cooking process for the cells in the top sheet to expand.

In a similar embodiment, the bottom side of a pouch formed of theinsulating microwave packaging material may be augmented by the additionof a sheet of the insulating microwave packaging material. In thisconfiguration, the susceptor layer forms the interior walls of thepouch. The second clear polyester layer of the sheet is placed againstthe clear polyester layer on the bottom side of the pouch and adhered inlocations to minimize any restriction of movement by the sheet in theX-Y dimensions. Alternatively, the pouch may be merely a susceptor pouchwith a sheet of insulating microwave packaging material attached to thebottom side of the pouch. The interior of the pouch is lined with asusceptor film, and again the susceptor layer of the sheet is orientedtoward the floor or turntable of the microwave oven. The insulatingmicrowave packaging sheet enhances the cooking ability of the susceptorpouch by insulating it from the heat sink of the microwave oven floor orturntable.

In a further embodiment of the invention, the dual sheet configurationof the microwave packaging material described above is combined with anyof several known baking substrates. In a preferred example, an apertureis formed in an abuse-tolerant microwave baking substrate and one or twosheets of the insulating microwave packaging material are arranged tocover the aperture. In this manner, the insulating microwave packagingmaterial of the present invention provides increased insulation betweena portion of the food product and the microwave oven surface andincreased contact between the susceptor and the and that portion of thefood product.

In yet another embodiment of the invention, a layer of an amorphouspolyester is pattern bonded along bond lines creating closed cells to apaperboard substrate. A susceptor film is laminated to the opposite sideof the paperboard substrate. Upon heating, the heated water vaporescapes from the paperboard creating pressure in the cells on the layerof amorphous polyester. The amorphous polyester expands and each cellforms a pillow-like bump on the surface on the paperboard. The bondlines may be designed to form cells of very small area to create asurface of very small bumps over the paperboard upon heating. Thissurface may be used to insulate the consumer from hot packaging whenholding the food product in the package after cooking.

In a further embodiment, a microwave package combines a carton form anda pouch formed of microwave interactive material, for example asusceptor or the insulating microwave packaging material of the presentinvention. The carton form has a base with a central fold line, a firstside wall hinged to the base along a first fold line, and a second sidewall hinged to the base along a second fold line. The pouch is supportedby the carton form and positioned between the base, the first side wall,and the second side wall. The carton form and the pouch may bealternately folded flat and erected to open the pouch. When the cartonform is erected by opening the folded base into a V-form, the base maybe inverted and the carton form is braced open by the base which is heldopen in tension between the first side wall and the second side wall.The first fold line and the second fold line may be convexly curved sothat, upon inverting, the base of the carton form assumes a concavelycurved form with the first side wall and the second side wall of thecarton form bowed or convexly curved. The pouch may be affixed to thefirst side wall and the second side wall of the carton form, forexample, by adhesive.

In another embodiment of the invention, a microwave cooking container isprovided where the body of the container includes a microwaveinteractive material. The body has a first end containing an apertureand a second end also containing an aperture. A food product is at leastpartially surrounded by the body. The first end provides a foundationfor maintaining the container in an upright position when the first endis placed upon a surface. The first aperture in the first end ispositioned to be exposed to a source of air in a cooking environmentwhen the first end is placed upon the surface. A draft is created duringa cooking cycle in a microwave oven wherein air is ported through theaperture in the first end and vented through the aperture in the secondend.

Other features, utilities and advantages of various embodiments of theinvention will be apparent from the following more particulardescription of embodiments of the invention as illustrated in theaccompanying drawings and defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an isometric view of a food product packaged in a ventedpackage of microwave interactive material.

FIG. 1B is an isometric view of the vented package of FIG. 1A in theprocess of being surrounded by an insulating material.

FIG. 1C is an isometric view of the vented package of FIG. 1A surroundedby an insulating material.

FIG. 2A is an exaggerated elevation, in cross-section, of an exemplaryembodiment of the insulating microwave interactive packaging material ofthe present invention before the packaging is subjected to microwaveenergy in an operating microwave oven.

FIG. 2B is an isometric view, in cross-section, of the insulatingmicrowave interactive packaging material of FIG. 2A before the packagingis subjected to microwave energy in an operating microwave oven.

FIG. 2C is an isometric view, in cross-section, of the insulatingmicrowave interactive packaging material of FIG. 2A after the packagingmaterial is subjected to microwave energy in an operating microwaveoven.

FIG. 2D is an exaggerated elevation, in cross-section, of an alternativeembodiment of the insulating microwave interactive packaging material ofthe present invention before the packaging is subjected to microwaveenergy in an operating microwave oven.

FIG. 3A is an isometric view of the bottom of a sheet of insulatingmicrowave interactive packaging material with a hexagonal adhesivepattern according to a second embodiment of the present invention beforethe packaging is subjected to microwave energy in an operating microwaveoven.

FIG. 3B is an isometric view of the top of the sheet of insulatingmicrowave interactive packaging material with the hexagonal adhesivepattern of FIG. 3A after the packaging is subjected to microwave energyin an operating microwave oven.

FIG. 4A is a plan view of an unassembled carton employing sheets ofinsulating microwave interactive packaging material according thepresent invention on the top and bottom interior surfaces of the carton.

FIG. 4B is a plan view of the unassembled carton of FIG. 4A furthershowing slits cut in the sheets about the perimeter to augmentcontraction of the sheets in the X and Y dimensions during microwaveheating.

FIG. 4C is an isometric view of the carton of FIG. 4A assembled with acutaway portion showing the sheet of insulating microwave interactivepackaging material on the bottom interior surface of the carton.

FIG. 4D is an isometric view of the carton of FIG. 4C with a cutawayportion showing the sheet of insulating microwave interactive packagingmaterial on the both the top and bottom interior surfaces of the cartonafter microwave heating.

FIG. 5 is an isometric view of an envelope of insulating microwaveinteractive packaging material surrounding a food product according to athird embodiment of the present invention after the packaging issubjected to microwave energy in an operating microwave oven.

FIG. 6 is an elevation of two sheets of insulating microwave interactivepackaging material fastened together at points along the perimeter ofthe sheets according to a fourth embodiment of the present inventionafter the packaging is subjected to microwave energy in an operatingmicrowave oven.

FIG. 7A is a top plan view, in partial cross-section, of two sheets ofinsulating microwave interactive packaging material fastened togetherwithin an aperture in a baking disk with a hexagonal adhesive patternaccording to a fifth embodiment of the present invention. The susceptorfilm and paper substrate of the upper sheet are partially cut away toreveal the adhesive pattern. The lower sheet is not visible.

FIG. 7B is a top plan view, in partial cross-section, of two sheets ofinsulating microwave interactive packaging material fastened togetherwithin an aperture in a baking disk with an adhesive pattern definingpartial sectors of a circle according to a sixth embodiment of thepresent invention. The susceptor film and paper substrate of the uppersheet are partially cut away to reveal the adhesive pattern. The lowersheet is not visible.

FIG. 8 is an exaggerated elevation, in cross-section, of abuse-tolerantmicrowave packaging used in conjunction with the embodiments of FIGS. 7Aand 7B.

FIG. 9A is an isometric view of a closed pouch of insulating microwaveinteractive packaging material according to another embodiment of thepresent invention.

FIG. 9B is a top plan view of the closed pouch of FIG. 9A.

FIG. 9C is a partial isometric view of the closed pouch of FIG. 9Aflipped top to bottom.

FIG. 10A is an exaggerated elevation, in cross-section, of anotherembodiment of the insulating microwave interactive packaging material ofthe present invention before the packaging material is subjected tomicrowave energy in an operating microwave oven.

FIG. 10B is an isometric view, in cross-section, of the embodiment ofFIG. 10A after the packaging material is subjected to microwave energyin an operating microwave oven.

FIG. 10C is an isometric view of a further embodiment of the insulatingmicrowave interactive packaging material of the present invention afterthe packaging material is subjected to microwave energy in an operatingmicrowave oven, wherein the packaging material of FIG. 10A is formedinto a container.

FIG. 11A is a plan view of a sheet of insulating microwave interactivematerial according to the present invention with elongate cells andindicating the adhesive bond line pattern.

FIG. 11B is plan view of a sheet of insulating microwave interactivematerial according to the present invention with elongate cells andindicating areas where the microwave interactive material isinactivated.

FIG. 12A is a plan view of a sheet of insulating microwave interactivematerial according to the present invention with elongate cells andindicating the adhesive bond line pattern.

FIG. 12B is a plan view of a sheet of insulating microwave interactivematerial according to the present invention with elongate cells andindicating areas where the microwave interactive material isinactivated.

FIG. 13A is an isometric view of a cooking pouch constructed of a sheetof insulating microwave interactive material of FIGS. 12A and 12B.

FIG. 13B depicts the cooking pouch of FIG. 13A after microwave heating.

FIG. 13C depicts the cooking pouch of FIG. 13B in cross section asindicated in FIG. 13B. The cross section is exaggerated to detail thevarious layers of the insulating microwave interactive material.

FIG. 13D depicts the cooking pouch of FIG. 13B in cross section asindicated in FIG. 13B.

FIG. 14A is an isometric view of a collapsible cooking package in itscollapsed position holding the cooking pouch of FIG. 13A without a foodproduct.

FIG. 14B is an isometric view of the collapsible cooking package of FIG.14A in its functional position holding the cooking pouch of FIG. 13Afilled with a food product.

FIG. 15A is a plan view of a sheet of insulating microwave interactivematerial according to the present invention with triangular elongatecells and indicating the adhesive bond line pattern.

FIG. 15B is a plan view of a sheet of insulating microwave interactivematerial according to the present invention with triangular elongatecells and indicating areas where the microwave interactive material isinactivated.

FIG. 15C is an isometric view of a cooking pouch formed of two sheets ofthe insulating microwave interactive material of FIGS. 15A and 15B.

FIG. 15D is an elevation view of the open end of the cooking pouch ofFIG. 15C.

FIG. 16 is an isometric view, in cross-section, of a microwavablepackage according to the present invention designed to promote airflowthrough the package.

FIG. 17 is an elevation view of a microwavable package according to thepresent invention designed for ease of handling by a consumer.

FIG. 18 is an elevation view, in cross-section, of a microwavablepackage according to the present invention design for ease of handlingby a consumer.

FIG. 19 is an elevation view of a microwavable package according to thepresent invention also designed for ease of handling by a consumer.

FIG. 20 is a top plan view, in cross-section, of another embodiment of amicrowavable package according to the present invention with acorrugated susceptor.

FIG. 21 is a chart depicting the differences in temperature during aheating cycle inside a package alternately lined with a regularsusceptor material and the insulating susceptor material of the presentinvention.

DESCRIPTION

This invention enhances the ability of microwave interactive packagingto improve microwave cooked food quality, when that quality relates tosurface browning (i.e., the Maillard reaction), crisp texture, andinternal moistness, through the insulation of the microwave interactivepackaging. Certain types of microwave interactive material, for example,susceptor material, utilize microwave electromagnetic energy to generatepackage surface heat. The metallized, thin-film susceptor is a poorelectrical conductor and generates heat like any resistance heater. Thepurpose of microwave susceptor packaging is to create surface heat tobrown and crisp food product that it contacts during the microwavecooking process.

Through the addition of an insulating material surrounding thesusceptor, more of the sensible heat generated by the susceptor istransferred to the surface of the food product rather than to themicrowave oven environment. Without the insulating material, much of theheat generated by the susceptor is lost via conduction into thesurrounding air and other conductive media, such as the microwave ovenfloor. When more of the sensible heat generated by the susceptor isdirected to the food product, browning and crisping results areenhanced.

It is also important to retain moisture present in food when cooling inthe microwave oven. Typical consumer complaints of “rubber microwavefood” or edges hard as a rock are the result of moisture loss. Theinsulation works with the susceptor package to help retain more moistureand thus enhance food texture and flavor.

Examples of typical microwave packages with susceptors include a paperpouch lined with a susceptor film and a paperboard sleeve lined with asusceptor film. Insulating material for surrounding these microwavepackages may be provided by many materials. Examples include cloth,paper towels, non-woven substrates, corrugated paper and paperboard,quilted paper and towels, heat resistant multi-layer films formed withair pockets (e.g., bubble wrap and the insulating microwave packagingmaterial disclosed herein), glass fiber, air cell foams, air cell gels,air cell rubber, cook-in cartons designed to retain heat, and any othermaterial that can surround the susceptor and create a heat barrier.

Some examples of typical food items that benefit from susceptorpackaging (either paper or paperboard construction) are: raw dough orpartially baked dough foods, for example, pizza, filled pastrysandwiches and “finger” foods, waffles, crusted pies (fruit or meat),egg rolls, calzones, tacos, and pastry puffs; and “fried” foods, forexample, whole muscle and processed meats (e.g., fish and poultry) andother items like French fries, cheese, mushrooms, and vegetables.

Insulation of Microwave Packaging Materials

As depicted in FIG. 1A, a food product 130, for example, a calzone, isplaced within a microwave interactive pouch package 100 for cooking. Themicrowave interactive pouch package 100 may be a paper pouch 108 linedon the interior side with a susceptor film 105. In this configuration,the susceptor film 105 is placed adjacent to the food product 130 topromote browning and crisping of the pastry shell. The paper 108provides a dimensionally stable substrate to support the susceptor film105.

The microwave interactive package 100 may also be designed to holdmoisture so the food product 130 does not dry out and harden, especiallyon the edges. In order to retain moisture, the edges 124 of themicrowave interactive package 100 are sealed, for example, with a heatseal wherein the opposing sides of the interior of the pouch lined withsusceptor film 105 are laminated around the edges 124. However, the foodproduct 130 should not be cooked with the pouch 100 completely sealedbecause the pouch may inflate from water vapor released by the foodproduct 130 during cooking, causing the susceptor film 105 to losecontact with the surface of the food product 130. To prevent suchinflation, a small vent opening 126 may be cut in the pouch 100, forexample, in a corner, to allow some small “controlled” venting to occur.However, some moisture retention may be desirable to prevent the foodproduct 130 from drying out during the cooking process. Therefore, abalance must be struck to prevent excessive vapor venting.

Next, an insulating material 140 is placed around the microwaveinteractive pouch 100 by, for example, folding the insulating material140 as indicated by the arrows shown in FIGS. 1B and 1C. The insulatingmaterial 140 may be as simple as a paper towel. The insulating material140 is folded over and around all sides of the pouch 100, including overthe vent opening 126, to surround the microwave interactive packaging100. The insulating material 140 may completely surround the packaging100, or it may be selectively placed on or around portions of thepackaging 100 to achieve any particular desired insulating effect. Theinsulating material 140 may further be moistened, for example, bydampening with water, to prevent excessive moisture loss and extend thecooking time available for the susceptor to brown and crisp the surfaceof the food product.

Experimentation

Experiments were conducted to verify the enhanced cooking effectsachieved by adding insulation to microwave interactive packaging duringthe microwave cooking process. In one experiment, two calzones wereplaced in paper cooking pouches lined with susceptor film, similar tothe pouch depicted in FIG. 1A. The purpose of this experiment was todetermine if browning and crisping of a calzone can be enhanced byutilizing insulation around the susceptor-lined cooking pouch during themicrowave cooking process. Pouches were used for this test (instead ofpaperboard sleeves) because of the ability of a pouch to conform betterto the irregular shape of the calzone product. The edges of the poucheswere heat sealed and a vent opening was cut in a corner of each pouch.The first pouch was then wrapped in a paper towel, similar to thedepictions in FIGS. 1B and 1C, to provide insulation around the cookingpouch. The second pouch was not insulated and was placed in themicrowave oven following the package instructions to place the foodproduct directly into the microwave oven on a plate.

Frozen calzones were cooked in the pouches for 2 minutes and 30 seconds.The calzones were then removed from the pouches and subjectivemeasurements were recorded. The first calzone cooked in the pouchinsulated by the paper towel resulted in a much crisper outer pastrysurface and enhanced browning than the second calzone that was notinsulated during cooking. The surface of the calzone cooked in theinsulated pouch reflected light (i.e., was shiny) indicating a glazedcrispness whereas the second calzone absorbed light indicating soft,soggy, porous surface. These results indicate browning and crisping areimproved by using an insulating “wrap” over susceptor cooking packages.

Two pizzas were cooked in a microwave oven under similar circumstances.The first pizza was placed on a standard susceptor covered paper bakingtray and was then wrapped in paper towels. The second pizza was alsoplaced on a standard susceptor covered paper baking tray without theaddition of insulating material. The crust on the bottom and edges ofthe first pizza cooked using insulation achieved greater browning andcrisping than the second “control” pizza.

In a further experiment, a raw dough fruit pie was placed in aMicroFlex®Q (Graphic Packaging Corporation, Golden, Colo.) microwavecooking pouch that completely surrounded the pie crust. A MicroFlex®Qpouch is made of two paper-backed susceptor film sheets, wherein theedges of the sheets are sealed together to form a pouch. The susceptorfilm of one of the sheets is formed in a grid pattern, wherein thegridlines are devoid of metallization, in order to reduce browningeffects of the susceptor film. The side of the pouch with the gridsusceptor is usually placed on the top side of the pie to prevent anoverdone top crust. The pouch with the pie was then placed in a plainpaperboard pie tray for support. The tray and pie were then completelywrapped three times with a paper towel for insulation. The insulationwrapped pie was then placed in a microwave oven for cooking. The resultsof this experiment were very positive. The pie crust was crisp andgolden after 16 minutes cooking time in a microwave oven.

Another series of experiments was performed cooking Tyson® SouthernStyle Chicken Nuggets in a 700 watt microwave oven. In each test, fourchicken nuggets were cooked in multiple sessions (four new nuggets werecooked in each session) of varying amounts of time in various packagingconfigurations for comparison of cooking results. For each cookingsession, a number of variables were recorded. These variables includedthe cooking time of the cooking session; the starting weight of the fournuggets; the weight of the four nuggets after cooking for the indicatedtime; the calculated weight loss between the before and after cookingweights; the weight loss as a percentage of the original weight; and theinternal temperature of the nuggets after cooking for the specifiedcooking time. These values are set forth in the tables below for eachcooking session performed with each packaging configuration. In certaintests, a particular cooking time was repeated for a second session toensure consistency in results. In addition, comparisons of subjectivequalities of cooking results between the tests, for example, levels ofbrowning, crisping, and moisture, were recorded and are set forth below.

Test 1—Control. In Test 1, the chicken nuggets were placed on a paperplate in the microwave oven and cooked without benefit of a susceptorpackage or insulating covering. TEST 1 Starting Cooked Weight PercentInternal Cook Time Weight Weight Loss Weight Temperature (minutes) (oz)(oz) (oz) Loss (° F.) 0.5 1.711 1.708 0.003 0.2%  78-143 1.0 1.708 1.5470.161 9.4% 198-201 1.5 1.726 1.405 0.321 18.5% 180-192 1.5 1.794 1.4680.326 18.2% 184-204 2.0 1.733 1.215 0.518 29.9% 201-207

Test 2—MicroFlex®Q pouch with multiple venting. In Test 2 the chickennuggets were placed in a pouch made of MicroFlex®Q material. Each sideof the pouch was sealed, but each of the four corners of the pouch wascut off to provide vent openings. TEST 2 Starting Cooked Weight PercentInternal Cook Time Weight Weight Loss Weight Temperature (minutes) (oz)(oz) (oz) Loss (° F.) 0.5 1.673 1.668 0.005 0.3%  60-154 1.0 1.724 1.6100.114 6.6% 188-198 1.5 1.953 1.604 0.349 17.9% 182-188 1.5 1.760 1.4500.310 17.6% 186-196 2.0 1.749 1.254 0.494 28.2% 201-203

When cooking the chicken nuggets within a susceptor-lined pouch withsubstantial venting, the internal temperature of the nuggets remainedgenerally constant. However, the nuggets in the pouch lost less weightdue to moisture loss during cooking, and therefore were more tender.

Test 3—MicroFlex® Q pouch with single vent. Test 3 was performed similarto Test 2, but only one of the four corners of the pouch was cut for avent opening. TEST 3 Starting Cooked Weight Percent Internal Cook TimeWeight Weight Loss Weight Temperature (minutes) (oz) (oz) (oz) Loss (°F.) 0.5 1.786 1.779 0.007 0.39%  30-165 1.0 1.802 1.677 0.125  6.9%174-193 1.5 1.748 1.489 0.259 14.8% 179-199 1.5 1.774 1.552 0.222 12.5%176-199 2.0 2.064 1.578 0.486 23.5% 178-200 2.0 1.771 1.337 0.434 24.5%150-202

When cooking the chicken nuggets in a susceptor-lined pouch with only asmall amount of venting, the moisture loss, and therefore the weightloss, of the nuggets during cooking was less than in either Test 1 orTest 2. The chicken in this instance was even more moist and tender onthe inside, while still achieving a brown and crisp surface.

Test 4—MicroFlex®Q pouch without venting. Test 4 used the same pouchesas in Tests 2 and 3, but no vent openings were cut into the pouch. TEST4 Starting Cooked Weight Percent Internal Cook Time Weight Weight LossWeight Temperature (minutes) (oz) (oz) (oz) Loss (° F.) 0.5 1.746 1.7430.003 0.2%  23-107 1.0 1.771 1.721 0.050 2.8% 163-192 1.5 1.771 1.5390.232 13.1% 180-202 1.5 1.727 1.508 0.219 12.7% 187-201 2.0 1.782 1.2680.514 28.8% 168-204

Test 4 produced similar weight loss percentages to Test 3, but withoutthe venting, the nuggets in Test 4 were not as brown and crisp on thesurface.

Test 5—Insulated MicroFlex®Q pouch with single vent. In Test 5, onecorner of the pouch was cut off for venting and the entire pouch waswrapped in three paper towel sheets for insulation and moistureretention. TEST 5 Starting Cooked Weight Percent Internal Cook TimeWeight Weight Loss Weight Temperature (minutes) (oz) (oz) (oz) Loss (°F.) 0.5 1.770 1.759 0.011  0.6%  25-104 1.0 1.763 1.666 0.097 5.50%138-193 1.5 1.778 1.492 0.286 16.1% 175-196 2.0 1.762 1.334 0.428 24.3%186-201

The moisture loss in Test 5, as shown by the percentage weight loss, wassimilar to the losses in Test 3 wherein another single vent pouch wasused. As such, the chicken meat remained moist and tender. However,because of the addition of the insulating paper towel, the chickennuggets of Test 5 attained greater browning and crisping levels than thenuggets of the previous tests.

Additional tests were conducted that show moisture loss can becontrolled even more by adding moisture to the insulating materialbefore the cooking process. By adding moisture to the insulatingmaterial, the cooking time may be effectively extended because ofreduced moisture loss in the food product and thereby even bettersurface browning and crisping may be attained.

Test 6—Moist insulation around MicroFlex®Q pouch with single vent. InTest 6, one corner of the pouch was cut off to provide a vent openingand the entire pouch was wrapped in three paper towel sheets moistenedwith water. TEST 6 Starting Cooked Weight Percent Internal Cook TimeWeight Weight Loss Weight Temperature (minutes) (oz) (oz) (oz) Loss (°F.) 1.5 1.772 1.666 0.106 6.0% 180-200 2.0 1.776 1.423 0.353 19.9%184-200 2.5 1.776 1.275 0.501 28.0% 186-204

At 1.5 minutes, good crispness of the battered surface of the chickennuggets was noted while the interior meat remained tender and moist. At2 minutes cooking time, the interior meat of the chicken nuggets wasstill soft, as evidenced by the low percent weight loss at this cookingtime as compared the percentage weight loss of nuggets in Tests 1-5after the same cooking period. In Test 6, an extra half minute ofcooking was possible before reaching a similar range of weight loss inthe nuggets experienced at 2 minutes in the previous tests. This allowedadditional time for the susceptor to brown and crisp the surface of thenuggets without drying out the meat.

Test 7—Moist insulation around MicroFlex®Q pouch without vent. In Test7, the same cooking configuration as Test 6 was used, with the exceptionthat no vent opening was provided in the pouch. TEST 7 Cooked PercentInternal Cook Time Starting Weight Weight Weight Temperature (minutes)Weight (oz) (oz) Loss (oz) Loss (° F.) 2.0 1.792 1.462 0.330 18.4%180-199 2.5 1.784 1.241 0.543 30.4% 194-203

After 2 minutes of cooking, some areas of the chicken nuggets werecrisp. All the nuggets appeared tender and moist on the inside. After2.5 minutes of cooking, the pouch self-vented on one side, splitting atthe seam to create a large opening (thus indicating the desirability forsome level of venting). At the 2.5 minute mark, the chicken nuggetsattained a good level of crispness, but were not as tender and moist asthe nuggets of Test 6 wherein a small vent opening was provided in thepouch.

While the benefits of insulating a microwave interactive package havebeen demonstrated above experimentally, a practical method for providingthese benefits to the consumer is desirable. In one embodiment, writteninstructions may be provided on the microwave interactive packaging fora food product directing the consumer to wrap the package in a papertowel, a cloth towel, or some similar insulating material before cookingthe food product in a microwave oven. The instructions couldadditionally direct the consumer to moisten the paper towel or otherinsulating material with water before wrapping it around the microwaveinteractive packaging. This instruction could further direct theconsumer to cut a vent opening in the microwave interactive packagingbefore surrounding the packaging with the insulating material.

Although providing instructions to the consumer may result in theaddition of insulating material to the microwave interactive packagingin some instances, it is not infallible. Some consumers fail to read orfollow the cooking instructions on the package. On other occasions, theconsumer will not have a suitable insulating material readily availablefor use with the packaging. In such instances, the result of cooking thefood product without the insulating material will be of lesser qualitythan if the directions for the addition of insulating material werefollowed, resulting in decreased consumer satisfaction with the product.

Self-Insulating Microwave Packaging Material

In general, a goal of product packaging is to provide the consumer witha product that is complete and easy to use. For many food products meantfor microwave cooking, it is desirable that the food product can becooked in the microwave oven in its original packaging to provide easeof use and time savings to the consumer. Product packaging should alsonot be bulky, but compact and uniform for ease of stacking and shipping.Low bulk packaging also reduces shipping and display costs because lessspace is required in trucks or other transport containers or for shelfdisplay.

An insulating microwave packaging material 200 according to the presentinvention for use in consumer food product packaging is depicted inFIGS. 2A, 2B, and 2C. The microwave packaging material 200 is thecombination of several different material layers. A susceptor film 205,which may be the product of the deposition of a thin layer of microwaveinteractive material 204 on a first plastic film 202, is bonded, forexample, by lamination with an adhesive 206 to a dimensionally stablesubstrate 208. The dimensionally stable substrate 208 is then bonded toa second plastic film 210. In an alternative embodiment depicted in FIG.2D, an additional substrate layer 230 may be adhered, for example withadhesive 232, to the first plastic film 202 opposite the microwaveinteractive material 204. This additional substrate layer 230 may be alayer of paper, which is provided to control the possible disintegrationof the susceptor film 205 during heating. In certain circumstances, thesusceptor film 205 may experience crazing under the extreme heat itgenerates and flakes of susceptor film 205 may peel away from thedimensionally stable substrate 208. The additional substrate 230prevents any such flakes of the susceptor film 205 from failing into thefood product.

The bond between the dimensionally stable substrate 208 and the secondplastic film 210 is in the form of a pattern, for example, a pattern ofadhesive 212, that creates a plurality of closed cells 214. Resistanceto vapor migration results as the closed cells 214 are bounded by thefirst plastic film 202, the adhesive 206, the adhesive pattern 212, andthe second plastic film layer 210, each of which are resistant to vapormigration. To maximize the sealing of the cells, it may be desirable toachieve an adhesive bond directly between the susceptor 205 and thesecond plastic film 210, for example, by choosing an adhesive for theadhesive pattern 212 that may penetrate the dimensionally stablesubstrate 208 and contact the first adhesive layer 206 on the susceptorfilm 205.

The microwave packaging material 200 presents as a substantially flat,multi-layered sheet as shown in FIG. 2B. Such a flat configuration isdesirable for use in packaging because it adds little bulk to thefinished package. Upon heating in a microwave oven, with a minorconstraints applied periodically about the perimeter of the sheet,several changes occur in the insulating microwave packaging 200 thatprovide several novel benefits. FIG. 2C depicts, in cross-section, themicrowave packaging material 200 of FIGS. 2A and 2B subjected tomicrowave energy in a microwave oven. As the susceptor film 205 heatsupon impingement by microwave energy, water vapor and other gasesnormally held in the paper substrate 208, and any air trapped in thethin space between the second plastic film 210 and the paper substrate208 in the closed cells 214, expand due to the heat generated. Theexpansion of water vapor and air in the closed cells 214 appliespressure on the susceptor film 205 and the paper substrate 208 on oneside, and the second plastic film 210 on the other side of the closedcells 214. However, each side of the microwave packaging material 200forming the closed cells 214 reacts simultaneously to the heating andvapor expansion in a unique way. The cells 214 expand to form a quiltedtop surface 220 of pillows 216 separated by channels 218 in thesusceptor film 205 and paper substrate 208 lamination, which lofts abovea bottom surface 222 formed by the second plastic film 210. Thus, anoriginally compact packaging material is transformed into a bulkinsulating material, without any further requirements for consumerpreparation of the food product package before cooking. This effectoccurs within 1 to 10 seconds in an energized microwave oven.

Several benefits of the pillows 216 formed by expansion of the closedcells 214 in the microwave packaging material 200 are observed. First,the water vapor and air pockets in the closed cells 214 providesignificant insulation between the food product in the microwavepackaging material 200 and the interior surfaces of the microwave oven.The base of a microwave oven, for example, the glass tray found in mostmicrowave ovens, acts as a large heat sink, absorbing much of the heatgenerated by the susceptor film 205 or within the food product itself.The vapor pockets in the pillows 216 formed by the present invention maybe used to insulate the food product and susceptor film 205 from themicrowave oven surfaces and the vented air in the microwave oven cavity,thereby increasing the amount of heat that stays within or istransferred to the food product. Second, the formation of the pillows216 allows the microwave packaging material to more closely conform tothe food product, placing the susceptor film 205 in closer contact withthe food product. This close contact enhances the ability of thesusceptor film 205 to brown and crisp the surfaces of the food productby conduction heating in addition to some convection heating of the foodproduct. Several examples of these benefits with regard to particularfood products are described herein below.

In an exemplary process for manufacturing the unique insulatingmicrowave packaging material 200, a biaxially-oriented polyestersubstrate, for example, 48-gauge polyester film web, is covered with amicrowave interactive material 204, for example, aluminum, to create astructure that heats upon impingement by microwave energy. However, anysuitable lossy substance that will convert microwave radiation into heatenergy in a microwave oven can be used as the microwave interactivematerial 204. Such substances fall primarily into four groups:conductors, semi-conductors, ferromagnetic materials, and dielectricmaterials. Preferred microwave interactive materials used in the presentinvention to form microwave interactive layer 204 are compositionscontaining metals or other materials such as aluminum, iron, nickel,copper, silver, carbon, stainless steel, nichrome, magnetite, zinc, tin,iron, tungsten and titanium. These materials may be used in a powder,flake or fine particle form.

Such a microwave interactive material layer when combined with adimensionally stable substrate 208, for example, paper, is commonlyknown as a “susceptor.” The polyester-aluminum combination alone isreferred to herein as a “susceptor film.” Other types ofbiaxially-oriented, plastic film 202 may also be substituted for thepolyester film. When aluminum is used to create the microwaveinteractive layer of a susceptor film 205, it may be applied to thepolyester substrate, for example, by sputter or vacuum depositionprocesses, to a thickness of between 50 and 2,000 angstroms. Exemplaryembodiments of susceptors that may be used in the context of thisinvention include MicroFlex®Q, MicroRite® (Graphic PackagingCorporation, Golden, Colo.), and the susceptors described in U.S. Pat.Nos. 4,641,005; 4,825,025; 6,133,560; and 6,414,290.

In one embodiment of the invention, the areas of the microwaveinteractive material layer 204 directly corresponding to the adhesivepattern 212 to be applied may be inactivated. U.S. Pat. Nos. 4,865,921;4,883,936; and RE34,683, each of which is hereby incorporated herein inits entirety, describe various processes for selective and patternedinactivation of microwave interactive materials. Inactivating themicrowave interactive material layer 204 opposite the adhesive pattern212, provides several benefits. The adhesive pattern 212 is more likelyto maintain a strong bond between the dimensionally stable substrate 208and the second plastic film 210 because the extreme heat generated bythe microwave interactive material layer 204 is not acting directly onthe adhesive and potentially weakening its constitution. A strongeradhesive bond results in a better vapor barrier forming the cells 214and better pillowing effects upon heating. Greater options for possibleadhesives are also available because the temperature requirements formaintaining adherence are reduced. Further, because the microwaveinteractive material layer 204 is removed from the perimeters of thecells 214, upon the contraction of the second plastic film layer 210 andthe formation of the pillows 218, ribs that are cool to the touch of auser may be formed opposite the channels 218. These cool to the touchpatterned surfaces allow a user to comfortably hold the food product inthe packaging while the food product and the packaging are still quitehot from the microwave cooking process. This embodiment is described ingreater detail herein with respect to FIGS. 11A 13D.

Conventional printing techniques such as rotogravure, flexography, silkscreening, and lithography may be used to treat the selected area of themicrowave interactive layer 204 with an inactivating chemical. Ingeneral, a wide variety of chemicals may be used to reduce or eliminatethe heat-generating capability of microwave interactive layer 204. Ithas been found that aqueous solutions of chelating agents, solutions ofZr⁺⁴, amines and hydroxyamines, dilute acids, and bases and solutions ofmetal salts are useful in reducing or eliminating the microwaveinteractive properties of microwave interactive layer 204. Examples ofchelating agents are ethylenediaminetetracetic acid (EDTA),diethylenetriaminepentacetic acid (DTPA) andhydroxyethylenediaminetriacetic acid (HOEDTA). Solutions of Zr⁺⁴ usefulin the present invention may include ammonium zirconium carbonate,sodium zirconium lactate, ammonium zirconium lactate, and zirconiumtartrate. Examples of amines and hydroxyamines useful in the presentinvention include ethanolamines, choline and salts thereof. Acids usefulin the present invention include acetic, formic and other organic acidsas well as dilute mineral acids such as hydrochloric acid, hydrofluoricacid and mixtures thereof. Examples of dilute bases useful in thepresent invention include potassium hydroxide, sodium hydroxide, lithiumhydroxide, sodium and potassium carbonates, and sodium and potassiumphosphates. Solutions of salts such as ferric chloride, sodium citrate,sodium tartrate, ferric sulphate, ferrous chloride, ferrous ammoniumsulphate, ammonium fluoride, sodium fluoride, zinc chloride, zinc oxideand zinc fluoride are examples of salt solutions useful in the presentinvention.

Sodium hydroxide is the preferred material used to treat microwaveinteractive layer 204 in accordance with the present invention,particularly when aluminum metal is the microwave interactive materialmaking up the microwave interactive layer 204. The pH of solutions ofsodium hydroxide used to inactivate portions of the microwaveinteractive layer 204 preferably ranges from about 7.5 to about 13 andis more preferably maintained in the range of about 8.5 to about 11. Fora commercial process, the sodium hydroxide solution used to treat analuminum microwave interactive layer is at room temperature although thetemperature may be higher or lower than normal room temperature.

It is generally also advantageous to add a small amount of surfactant tosolutions of an inactivating chemical used to treat the microwaveinteractive layer to improve the wetting characteristics of the chemicaland the subsequent reaction of the chemical with the microwaveinteractive layer. Examples of surfactants which may be used includeCERFAK 1400™ produced by E. F. Houghton, KATAMUL-1G™ produced by ScherChemicals, Inc., IGEPAL-C0630™ produced by GAF Corporation and TRJTONX-100 produced by Rohm & Haas. A surfactant preferred for use inconjunction with sodium hydroxide is TRITON X-100™.

The mechanism by which chemicals modify treated portions of themicrowave interactivate layer without removing the layer is not knownfor every possible combination of chemical and microwave interactivematerial. It is believed, however, that aluminum is inactivated by avariety of chemicals which oxidize aluminum metal. It is possible,however that different chemicals will inactivate the microwaveinteractive layer by different mechanisms. Coordination, chelation,oxidation/reduction, and/or formation of salts of the microwaveinteractive material may contribute to or cause inactivation of aluminumand other suitable lossy materials.

The completed susceptor film 205 layer is next coated with an adhesive206, for example, a wet-bond adhesive, preferably on the aluminumdeposition layer, rather than the side with the exposed polyester, forcreating a laminate with at least one other substrate layer. Bonding theadditional substrate to the aluminum deposition allows the polyester toact as a protective layer over the microwave interactive aluminum 204,rather than exposing the aluminum side in the finished product. Thislamination step adheres the susceptor film 205 to adimensionally-stable, packaging substrate 208, for example, paper,paperboard, or a plastic substrate. If the chosen substrate is paper orpaperboard, a wet bond adhesive is preferably used; if the substrate isa plastic, a dry bond adhesive is preferred. Typical types of papersubstrates that may be used with this invention range between 10 lb and100 lb paper, for example, 25 lb paper. Typical ranges for paperboardsubstrates that may be used with the present invention include 8-pointto 50-point paperboard.

Similarly, plastic substrates of between 0.5 mils and 100 mils thicknessare also applicable. Appropriate plastic substrates are polymers thatrespond in a similar manner to the paper substrates. Particularly, theplastic substrate should be easily pliable to distort and move with thesusceptor film 205 as it heats and bulges. To maintain the desireddimensional stability, a plastic substrate should have a highersoftening point than the plastic used to create the susceptor film 205.For example, when used to support a susceptor film 205 with an aluminumdeposition as the microwave interactive layer 204, the plastic substrateshould be able to withstand temperatures in the range of 350° F. to 425°F. without melting, burning, or otherwise disintegrating.

As used herein, “dimensionally-stable” when describing a substrate 208refers to the interface of the substrate 208 and the susceptor film 205.Dimensionally-stable indicates a substrate 208 that will not soften,melt, or flow when subjected to the heat generated by the microwaveinteractive material 204. However, “dimensionally stable” does not meanthat a substrate 208 is not malleable or may not be deformed from anoriginal shape or configuration. The purpose of a dimensionally stablesubstrate 208 is to prevent the susceptor film 205 from disintegrating(e.g., by the melting of the plastic film 202) upon heating.

A second lamination step completes the manufacturing process. A furtherlayer of adhesive 212 is applied to the substrate 208 in a pattern. Asecond layer of polyester film 210 is then adhered to the substrate 208.The adhesive pattern 212 renders a nested array of closed cells, whereinthe perimeters of adjacent cells are shared borders. The adhesive 212may be chosen to penetrate the paper substrate 208 and contact the firstadhesive layer 206, thereby creating cells 214 bounded by the adhesivepattern 212, the first adhesive layer 206 and the adjacent susceptorfilm 205, and the second polyester film 210. The cells 214 thus created,which each encapsulates a portion of the paper substrate 208, aresubstantially vapor-impermeable and air-tight, thereby holding in theexpanding water vapor and air during heating. The air trapped in eachcell 214 is generally minimal as most of the air is evacuated when thesecond polyester film 210 is pressed against the paper substrate 208 inthe lamination process. The amount of moisture trapped in the papersubstrate 208 and the cells 214 will influence the amount of cellexpansion upon heating. If merely the paper substrate 208 were one ofthe boundaries of the cells 214, much of the water vapor and air wouldescape through the porous bulk of the paper substrate 208, and theformation of pillows 216 in the microwave packaging material 200 wouldbe much less pronounced.

As indicated above, upon impingement by microwave energy in a microwaveoven, the microwave packaging material 200 undergoes a transformation.As the microwave interactive layer 204 heats due to the microwaveenergy, the first plastic film 202 supporting the microwave interactivelayer 204 becomes extremely hot, between 350° F. and 425° F. At such ahigh temperature, the first plastic film 202 softens and would flow wereit not supported by the substrate 208. At the same time, air trappedbetween the substrate 208 and the second plastic film 210 in the cells214 formed by the adhesive pattern 212, and water vapor retained in thesubstrate 208, for example, if the substrate 208 is paper, expand due tothe heat generated by the microwave interactive layer 204 and theexcitation of the water vapor by the microwave energy. This vaporexpansion creates pressure in the closed cells 214, and the susceptorside of the cells 214 bulges outward under the pressure. Because theplastic film 202 is softened by the heat, it is able to stretch anddistort with the substrate 208 under pressure.

Also simultaneously, the second plastic film 210 is heated, but not tothe same degree as the first plastic film 202 because the substrate 208and the expanding air and water vapor insulate the second plastic layer210 from the intense heat of the microwave interactive layer 204.Although softened by the heat, the second plastic layer 210 is not hotenough to flow and it either remains stable or, as in some embodimentsdescribed herein, actually contracts in surface area as a result of thebiaxial orientation, wherein the polymer chains attempt to contract totheir original state. The pressure of the expanding air and water vapor,therefore, presses upon the softened first plastic layer 202 and thepaper substrate 208, which expand over each cell 214 area to form watervapor pockets and air creating the pillows 216 on the top surface 220 ofthe microwave packaging material as shown in FIG. 2C. Defining eachpillow 216 are channels 218 where the patterned adhesive 212 holds thesusceptor film 205, the substrate 208, and the second plastic film 210together.

The second layer of polyester film 210 is preferably biaxially-orientedpolyester as is the first layer of polyester film 202. Biaxialorientation means the polyester film has been stretched in both the Xand Y directions during its manufacture resulting in uniformly alignedpolymer chains of molecules in the polyester film. The alignment ofpolymer chains creates additional strength in the polyester sheet, evenas it is stretched thinner. This increased strength is important to thecreation of the susceptor film 205, as the first polyester film 202 isbetter able to support the deposition of the aluminum microwaveinteractive layer 204. The increased strength of both the first andsecond polyester films 202, 210 also makes them easy to work with duringthe manufacture of the microwave packaging material 200.

The alignment of the polymer chains further increases the resistance ofthe polyester films 202, 210 to heat. The first polyester film 202 issubjected to very high temperatures when the microwave interactive layer204 heats upon impingement by microwave energy. The biaxial orientationof the polyester film 202 helps maintain the integrity of the susceptorfilm 205 by raising the heat distortion temperature of the polyesterfilm 202. When the heat distortion temperature is reached, thebiaxially-oriented polyester film 202 attempts to contract in the X-Ydirection as the polymer chains attempt to return to their originalform. However, because it is adhered to the dimensionally-stable papersubstrate 208, the polyester film 202 is unable to contract. Thepolyester film 202 does soften, however, allowing it and the papersubstrate 208 to yield and pillow-up under the pressure of the expandingwater vapor and air. Once formed into the pillow shape, the papersubstrate 208 is resistant to returning to its original flat form.

The heat resistant properties of the biaxial orientation of the secondpolyester film 210 result in a different effect for the second polyesterfilm 210. The second polyester film 210 is separated from the microwaveinteractive film 204 by the paper substrate 208, which also providesinsulation from the heat generated by the susceptor film 205. Therefore,the second polyester film 210 does not heat to the same degree as thefirst polyester film 202. Further, as the air and water vapor in eachcell 214 expand, the second polyester film 210 is further insulated fromthe heat generated. The heat transferred to the second polyester layer210 is not as great as the heat transferred to the first polyester film202. However, the heat transferred to the second polyester film 210 isenough to cause the polymer chains to contract in both the X and Ydirections, regressing toward the form of the polyester film 210 beforeit was stretched to produce the biaxial orientation. This contractioncreates a taught bottom surface 222 of the microwave packaging material200, which is more resistant to the pressure of the expanding watervapor, and enhances the pillowing effect on the top surface 220 of themicrowave packaging material in the Z direction.

The combination of the X-Y contraction of the second polyester film 210on the bottom surface 222 of the packaging material 200, the expansionof the air and water vapor in the cells 214, and the softening of thefirst layer of polyester film 202 together creates the quilted topsurface 220 of pillows 216 in the microwave packaging material 200,resulting in the unique attributes of the invention as depicted in FIG.2C. It should be noted that in actual practice, the amount and variationof pillowing, or Z-direction expansion may vary greatly. Such expansionwill be dependent upon the exact material properties of the microwavepackaging material 200, the manufacturing process, the moisture contentof the substrates, and packaging construction constraints that myrestrict X-Y direction contraction. The amount of Z-direction expansionalso greatly depends upon particular microwave oven conditions andvarious food load factors, for example, size, weight, and temperature.All of these factors combine to create a load factor that may not alwaysbe exceeded by the expansion factor of the microwave packaging materialto achieve the maximum benefit of the invention.

FIGS. 3A and 3B show an exemplary embodiment of many possible adhesivepatterns 312 for creating the cells 314 within the packaging material300. A hexagonal adhesive pattern 312, as shown in FIGS. 3A and 3B, isan excellent basic polygonal pattern to select due to its ability tonest perfectly with adjacent hexagons and its high degree of cylindricalsymmetry. Other shapes for use as adhesive patterns 312, for example,circles, ovals, and other curvilinear shapes, preferably symmetricalcurvilinear shapes, for example, multi-lobed flower shapes, triangles,squares, rectangles (as shown in FIGS. 2A and 2B), and other polygonalshapes, preferably right polygons, and even more preferably equilateralpolygons, are within the scope of the present invention. As used hereinthe term “symmetrical curvilinear shape” means a closed curvilinearshape that can be divided in half such that the two halves aresymmetrical about an axis dividing them. As used herein, the term “rightpolygon” means a polygon that can be divided in half such that the twohalves are symmetrical about an axis dividing them. Equilateral polygonswould therefore be a subset of right polygons.

These adhesive patterns 312 are preferably configured in arrays suchthat they are similarly capable of tiling or nesting as depicted in FIG.3A by the adhesive pattern 312 showing through the second plastic film310 on the bottom surface 322 of the packaging material 300. When heatedby microwave energy, the top surface 320 of the microwave packagingmaterial 300 expands and forms the pillows 316 and channels 318. Inaddition, the arrays of adhesive patterns 312 need not be repetitive ofa single shape, but instead can be combinations of various shapes,preferably capable of nesting or tiling together to share commonperimeters. For example, an array of shapes for an adhesive pattern 312might be an array of nested hexagons and polygons, as in the patchworkof a soccer ball.

FIGS. 4A, 4B, 4C, and 4D depict an exemplary embodiment of a microwavefood package 410 that employs two sheets 400 a, 400 b of the insulatingmicrowave packaging material of the present invention. The microwavefood package 410 may be a paperboard carton 402, shown as a blank inFIGS. 4A and 4B and shown assembled in FIGS. 4C and 4D. The carton 402may be formed of a bottom panel 404 a, a top panel 404 b, side panels406 a, 406 b, 406 c, 406 d, a bottom flap 408 a, a top flap 408 b,corner tabs 422 a, 422 b, 422 c, 422 d, and a back panel 426. A bottomtray of the carton 402 for holding a food item to be cooked is formedout of the bottom panel 404 a, the bottom flap 408 a, the back panel426, and the side panels 406 a, 406 b. The side panels 406 a and 406 bare folded upward along score lines 430 a and 430 b, respectively.Similarly, the bottom flap 408 a is folded upward along score line 428 aand the back panel is folded upward along score line 428 b. The bottomflap 408 a is secured to the side panels 406 a and 406 b by folding tabs422 a and 422 b along score lines 438 a and 438 b, respectively, andthen inserting tabs 422 a and 422 b into slots 424 a and 424 b,respectively. Similarly, the back panel 426 is secured to the sidepanels 406 a and 406 b by folding tabs 422 c and 422 d along score lines438 c and 438 d, respectively, and then inserting tabs 422 c and 422 dinto slots 424 c and 424 d, respectively.

A lid for the carton is formed out of the top panel 404 b, the sidepanels 406 c, 406 d, and the top flap 408 b. The top panel 404 b isfolded along score line 428 c to rest on the side panels 406 a and 406 band the bottom flap 408 a The side panels 406 c and 406 d are foldeddownward along perforation lines 432 a and 432 b, respectively, to restflat against side panels 406 a and 406 b, respectively. Similarly, thetop flap 408 b may be folded downward along score line 428 d to restflat against bottom flap 408 a. The top flap 408 b and the side panels406 c and 406 d may be secured to bottom flap 408 a and side panels 406a and 406 b, respectively, for example, with adhesive in order to securethe lid to the tray and hold the food item inside until the carton 402is opened by the user after cooking. The carton 402 may be easily openedby the user by pulling upward on the top flap 408 b. The top flap 408 band the top panel 404 b will rip open along perforation lines 432 a and432 b allowing the user easy access to the food item while maintainingthe integrity of the tray to hold the food item. Cutouts 434 a and 434 bmay be formed in top flap 408 b to aid in the initial tearing alongperforation lines 432 a and 432 b, respectively.

In this embodiment, the cells 414 of the sheets 400 a, 400 b are formedas squares by the adhesive pattern 412. The sheets 400 a, 400 b may beaffixed to the bottom panel 404 a and top panel 404 b of the carton 402with adhesive tacks 436. The adhesive tacks 436 may be placed at thecorners of the sheets 400 a, 400 b to allow for some movement of thesheets 400 a, 400 b as the polyester layer of the insulating microwavepackaging material shrinks during heating. Alternatively, centered slits440 a or off-centered slits 440 b be may be cut in the sheets 400 a, 400in close proximity to the perimeters between the adhesive tacks 436 toallow for even greater movement of the sheets 400 a, 400 b as thepolyester layer of the insulating microwave packaging material shrinksduring heating. The location and arrangement of slits 440 a and 440 band adhesive tacks 436 are exemplary and many other slit patterns andglue patterns may be used to allow for Z-directional expansion and X-Ydirectional contraction of sheets 400 a and 400 b. The adhesive used forthe tacks 436 may also be heat sensitive and release as the sheets 400a, 400 b heat under the excitation of microwave energy. By releasing,the sheets 400 a, 400 b are able to contract as necessary during heatingand allow the cells 414 to expand to form the pillows 416. The sheetsremain generally in place as they are constrained by the side panels 406a and 406 b, the bottom flap 408 a, and the back panel 426, as well asthe food item resting on the bottom sheet 400 a.

The formation of the pillows 416 by the sheets 400 a, 400 b of theinsulating microwave packaging material of the carton 402 providesseveral advantages over cartons using flat susceptor sheets or coatingson the interior panels of such cartons. The susceptor material pillows416 to become closer in proximity to the food item, especially to thetop surface of the food item as the sheet 402 b on the top panel formspillows 416. This provides for increased surface heating, browning, andcrisping of the top of the food item. Additionally, the air and watervapor in the pillows 416 provides added insulation, trapping heat in thecarton 402 and enhancing the cooking result of the food item. In oneexperiment, a carton with quilted susceptor sheets of the type shown inFIGS. 4C and 4D was used to cook French fries in a microwave oven. As acontrol, a carton with regular susceptor covered panels was used to cooka like amount of French fries for the same period of time. As shown inthe graph depicted in FIG. 21, the air temperature inside the carton 402during comparable 2.5 minute cooking periods maintained a trend ofbetween 15° F. and 50° F. higher than the carton with regular susceptorpanels due to the insulating properties of the insulating microwavepackaging material of the present invention.

Several advantages of the invention are also achieved by the embodimentdepicted in FIG. 5. In this embodiment a sheet of microwave packagingmaterial 500 according to the present invention is folded over on itselfwith the top surface 520 facing inward and the bottom surface 522composed of the second plastic film 510 facing outward. The two edges ofthe sheet of microwave packaging material 500 opposing the fold line 526are fastened together, for example, via heat sealing or adhesive, toform a sealed edge 524. The sheet of packaging material 500 is therebytransformed into an envelope or sleeve into which a food product 530,for example, a fruit pie snack, may be placed.

In the prior art a food product may rest on the base of a microwavepackage incorporating susceptor material, for example, a cooking sleeve,but the food product may not touch or be in close proximity with thesides or top of the package. While the bottom of the food product maybecome brown and crisp because of the contact between the packaging andthe food product, the sides and top of the food product will have lessbrowning and crisping because of lack of contact with the susceptormaterial. By using the present invention, as the susceptor film 505heats, the microwave packaging material 500 expands to form the pillows516 on the top surface 520, which bring the susceptor film 505 in closeproximity to or contact with the food product 530 on all sides,providing the desired cooking effect on all sides of the food product530. The channels 518 between the pillows 516 in the quilted top surface520 provide the added benefit of venting water vapor released from thefood product 530 during cooking, which further enhances the surfacebrowning and crisping effects of the susceptor film 505. The vaporfilled cells 514 further insulate the food product 530 from themicrowave oven and ensure the heat generated remains in the food product530 rather than transferring to the oven environment.

In other situations, the size and shape of a food product may varyand/or shrink during cooking and pull away from a susceptor positionedadjacent the food product. With the present invention, the insulatingmicrowave packaging material 500 may fill the void created by theshrinking food product with the expansion of the pillows 516 on the topsurface 520, maintaining the susceptor film 505 in constant contact withor close proximity to most surfaces of the food product 530. Some foodproducts, for example, bread dough, have the opposite tendency whilecooking and actually rise or expand. The microwave packaging material500 is also beneficial for use with such rising food products 530. Themicrowave packaging material 500 initially expands to meet the foodproduct 530 before the food product 530 has risen. As the food product530 rises, the microwave packaging material 500 has some give to yieldto the rising food product 530 as the pressure within the cells 514 fromthe heated water vapor is not so high as to fully resist such externalpressure. In practice, the vapor expansion in each of the plurality ofclosed cells 514 and the simultaneous contraction of the second plasticlayer 510 increases the thickness of the packaging material 500 by atleast an order of magnitude. Experiments with the various embodimentsdiscussed herein have resulted in expansion of the thickness of thepackaging material 500 by up to 30 times, providing for a snug fitaround food products 530.

As mentioned above, a novel benefit of the microwave packaging material200 of the present invention, as in FIGS. 2A-2C, is its ability toinsulate against heat transfer from the food product or the microwavepackaging material 200 itself to the microwave oven environment duringcooking. In normal microwave oven operation, the vented air in the ovencavity and the glass tray, or other cooking platform, act as large heatsinks, absorbing much of the heat generated by either the microwaveheating of the food product or the microwave interactive materials, forexample, susceptor materials, thereby lessening the ability of themicrowave packaging material to augment the heating and browning of thefood product. With the present invention, during cooking, the vapor andgases from the paper substrate 208 expand into the closed cells 214, asshown in FIG. 2C. These vapor pockets formed in the closed cells 214transform the microwave packaging material 200 into an insulator thatreduces heat transfer between the microwave packaging material 200 andthe microwave oven environment. These insulation qualities result inimproved performance of the heating properties of the susceptor film205.

In an exemplary embodiment shown in FIG. 6, the insulating properties ofthe present invention are enhanced over the embodiment depicted in FIGS.2B and 2C. In FIG. 6, a first sheet 600 a and a second sheet 600 b ofthe microwave packaging material are placed bottom side 622 a to bottomside 622 b, the second plastic film 610 a of the first sheet 600 afacing the second plastic film 610 a of the second sheet 600 b. Thesheets 600 a, 600 b may be tacked together, for example, by adhesive orheat seal, at several points 628 spaced apart from each other along theperimeters of sheets 600 a, 600 b. For example, if the sheets 600 a, 600b are square, the corners of the sheets 600 a, 600 b may be tackedtogether; if the sheets are round, several points spaced apart along theperimeter of the sheets may be chosen and the sheets tacked together atthose points.

Also, oftentimes a frozen food product placed upon a microwave ovensurface will cool the microwave oven surface before the microwave ovenis energized, increasing the amount of heat transfer to the microwaveoven surface once the cooking process begins. In the embodiment of FIG.6, as one of the two sheets of microwave packaging material, e.g., 600b, is in contact with the microwave oven surface, the susceptor film 605b heats the microwave oven surface while the susceptor film 605 a of theopposite sheet 600 a heats the food product, further reducing theability of the microwave oven surface to act as a heat sink. Further, inthe case of a frozen or cold food product, the bottom sheet 600 b of thedual sheet embodiment creates enough heat energy immediately to causethe vapor expansion in the cells 614 a, 614 b of both sheets of themicrowave packaging material 600 a, 600 b soon after the microwave ovenis energized. If there were only one sheet of microwave packagingmaterial, for example 600 a, the frozen food product would significantlyincrease the time required to heat the water vapor and air and achieveexpansion of the cells 614 a because the surface temperature of thesusceptor film 605 a will not rise until the surface temperature of thefood product accordingly rises.

The opposing sheets of packaging material 600 a, 600 b are only attachedat points 628 at their perimeters on the corners to allow for movementof the sheets 600 a, 600 b in the X and Y directions. When theback-to-back sheets 600 a, 600 b are exposed to microwave energy in amicrowave oven, the cells 614 a, 614 b expand in the Z direction, andthe second plastic film layers 610 a, 610 b contract in both the X and Ydirections as a result of the biaxial orientation of the plastic film610 a, 610 b as discussed above. Therefore, some freedom of movement inthe X-Y directions is desirable in order to achieve favorable expansionresults. It may be desirable, however, to provide some externalstructure to the microwave packaging material 600 a, 600 b, such asattachment points on the perimeters, to augment uniform shrinkage inboth the X and Y directions and minimize distortion or wrinkling of themicrowave packaging material 600 a, 600 b in any particular direction.For example, in experimentation with cells of about 1 in² in area, theelevation achieved by individual cells after microwave heating wasbetween 0.375 in and 0.5 in from a starting thickness of the insulatingmicrowave packaging material of less than 0.03125 in.

In addition to the expansion of individual cells 614 a, 614 b, theopposing sheets 600 a, 600 b also deform on a macro scale from theiroriginal flat, paper-like form. The first sheet 600 a deforms into aconvex canopy with respect to a plane dividing the first and secondsheets 600 a, 600 b. Similarly, the second sheet 600 b deforms into aconvex canopy with respect to the plane dividing the first and secondsheets 600 a, 600 b. As a result of the convex deformations of thesheets, an air space is created between the sheets 600 a, 600 bproviding greater than double the insulation of a single sheet,isolating the food product from the potential heat sink of the microwaveoven surface.

A particular packaging configuration using the principles of theembodiment of FIG. 6 is shown in FIG. 7A. A pizza baking disk 740 madeof an abuse-tolerant microwave packaging material of the type describedin U.S. Pat. No. 6,204,492 B1 issued 20 Mar. 2001 to Zeng et al., whichis hereby incorporated by reference as though fully set forth herein, ismodified to incorporate the insulating microwave packaging material 700of the present invention. It is a phenomenon of frozen pizza preparationand packaging that the perimeter of the pizza freezes before its center.As the perimeter freezes, the dough contracts and decreases slightly incircumference. This causes the as yet unfrozen center of the pizza,resting on a flat surface, to bulge upward, creating a pocket betweenthe center of the frozen pizza and any surface it later rests upon. Thiscauses great difficulty in achieving a desirable cooking outcome for afrozen pizza, even when using a baking disk 740 with susceptor materialbecause the center of the pizza is not in contact with the susceptor tobe crisped. Therefore, the centers of frozen pizzas often turn out soggyand undercooked.

By combining the present invention with a prior art abuse-tolerantbaking disk 740, this cooking limitation is overcome. An aperture 745may be made in the center of the abuse-tolerant baking disk 740, withinwhich a circular piece of the dual sheet embodiment (as described withreference to FIG. 6 herein) of the packaging material 700 is placed. Inone exemplary configuration, the sheets of packaging material 700 may beattached to each other, for example, at areas 728, allowing theperimeter edges of the sheets of packaging material 700 to sandwich asmall width of the perimeter of the abuse-tolerant baking disk 740defining the aperture 745 between each sheet, thus holding the packagingmaterial 700 within the aperture 745 in the abuse-tolerant baking disk740. In a second exemplary embodiment, each sheet of the packagingmaterial 700 may be fastened, for example with a heat sensitiveadhesive, to respective opposing sides of the baking disk 740 alongportions of the aperture 745. In this manner, the packaging material 700and the abuse-tolerant baking disk 740 are held together during thepackaging process. However, when subjected to the heat generated by thesusceptor film layers 705 of the packaging material 700, the heatsensitive adhesive may break down allowing the second plastic film 710of the packaging material 700 the necessary range of X-Y dimensionalmovement to optimize the expansion effect in the cells.

When heated by the impingement of microwave energy, the microwavepackaging material 700 expands, insulating the pizza from the heat sinkof the microwave oven surface and pushing the susceptor material intoclose contact with the raised center of the frozen pizza, therebyproviding increased heating, browning, and crisping to the center of thepizza. The benefit of the dual sheet embodiment of the microwavepackaging material 700 in creating immediate expansion of the cells whenused with a frozen food product as described previously is readilyapparent in the frozen pizza situation. The susceptor film 705 againstthe microwave oven surface also heats that surface, thereby additionallycounteracting its effects as a heat sink and allowing heat generated bythe susceptor film 705 against the pizza center to transfer only to thepizza.

In an alternative embodiment depicted in FIG. 7B, the cell areas 716 ofthe insulating new package material 700 are defined by an adhesivepattern 712 subdividing partial sectors of a circle (rather than thehexagonal pattern in FIG. 6) to capitalize on the circular configurationof the microwave packaging material 700 within the aperture 745 in theabuse-tolerant baking disk 740. Each sheet of the microwave packagingmaterial 700 is fastened as previously described to either the opposingsheet or the abuse-tolerant baking disk 740 at various areas 728, withthe susceptor film 705 sides facing outward, to aid in maintaining theperimeter shape of the microwave packaging material 700 during heating,while allowing for X-Y dimensional contraction of the second plasticfilm 710.

A cross-section of abuse-tolerant microwave packaging material 800 usedfor the baking disks of FIGS. 7A and 7B is shown in FIG. 8. Theabuse-tolerant packaging material 800 of this exemplary embodiment isformed of a polyester substrate 802 covered by a thin deposition ofaluminum 804 to create a susceptor film 805. When laminated incombination with a dimensionally stable substrate (e.g., paperboard) asis the ultimate result of the microwave packaging material 800, thepolyester substrate 802 and aluminum layer 804 function as a susceptor.The aluminum layer 804 is covered with a dry bond adhesive layer 806. Analuminum foil layer 808 is adhered to the susceptor film 805 via the drybond adhesive layer 806. Then a patterned ink resist coat 810 is printedon the foil layer 808, and the exposed foil layer 808 is etched away ina caustic bath. The resultant patterned foil layer 808 remaining afterthe etching process, shown in FIGS. 6 and 7, is covered by the patternedink resist coat 810. The patterned foil layer 808 and ink resist coat810 are covered by a second adhesive layer 812. For the sake ofdiscussion, in this embodiment the adhesive layer 812 is a wet bondadhesive. The adhesive layer 812 further covers the etched areas betweenthe patterned foil elements 808 and adheres in these areas to the drybond adhesive layer 806. The final component of this exemplaryembodiment is a dimensionally stable paperboard substrate 814 that isadhered to the previous layers by the second adhesive layer 812. Thus,the various layers are laminated together to form microwave packagingmaterial 800.

The abuse-tolerant microwave packaging material 800 forming the pizzabaking disk redistributes incident microwave energy by increasing thereflection of microwave energy while maintaining high microwave energyabsorption. A repeated pattern of metallic foil segments 808 can shieldmicrowave energy almost as effectively as a continuous bulk foilmaterial while still absorbing and focusing microwave energy on anadjacent food surface. The metallic segments 808 can be made of foil orhigh optical density evaporated materials deposited on a substrate 802.High optical density materials include evaporated metallic films thathave an optical density greater than one (optical density being derivedfrom the negative logarithm of the ratio of transmitted light toincident light). High optical density materials generally have a shinyappearance, whereas thinner metallic materials, such as susceptor films805 have a flat, opaque appearance. Preferably, the metallic segments808 are foil segments.

The metallic segments 808 may form segmented outlines of various shapes.Such shapes may be, for example, circles, ovals, and other curvilinearshapes, preferably symmetrical curvilinear shapes, for example,multi-lobed flower shapes, triangles, squares, rectangles, and otherpolygonal shapes, preferably right polygons, and even more preferablyequilateral polygons, are within the scope of patterns of theabuse-tolerant packaging material 800. The hexagon is an excellent basicpolygon to select due to its ability to nest perfectly along with itshigh degree of cylindrical symmetry. The shapes formed by the microwavereflective segments 808 are preferably configured in arrays such thatthey are similarly capable of tiling or nesting. In addition, the arraysof shapes need not be repetitive of a single shape, but instead can becombinations of various shapes, preferably capable of nesting or tilingtogether with small gaps between the metallic segments 808. For example,an array of shapes might be an array of nested hexagons and polygons, asin the patchwork of a soccer ball.

The segmented foil 808 (or high optical density material) structureprevents large induced currents from building at the edges of theabuse-tolerant packaging material 800 or around tears or cuts in theabuse-tolerant packaging material 800, thus diminishing the occurrencesof arcing, charring, or fires caused by large induced currents andvoltages. The abuse-tolerant design includes a repeated pattern of smallmetallic segments 808, wherein each segment acts as a heating elementwhen under the influence of microwave energy. In the absence of adielectric load (i.e., food), this energy generates only a small inducedcurrent in each element and hence a very low electric field strengthclose to its surface.

Preferably, the power reflection of the abuse-tolerant packagingmaterial 800 is increased by combining the abuse-tolerant packagingmaterial 800 with the susceptor film layer 805. In this configuration, ahigh surface-heating environment is created through the additionalexcitement of the susceptor film 805 due to the composite action of foodcontacting the small metallic segments 808. When the food contacts themetallic segments 808 of the abuse-tolerant packaging material 800, thequasi-resonant characteristic of perimeters defined by the metallicsegments 808 can stimulate stronger and more uniform cooking. Unlike afull sheet of plain susceptor film 805, the present invention canstimulate uniform heating between the edge and center portion of a sheetof the abuse-tolerant metallic segments 808 combined with a susceptorfilm 805 to achieve a more uniform heating effect.

The average width and perimeter of the pattern of metallic segments 808will determine the effective heating strength of the pattern and thedegree of abuse-tolerance of the pattern. However, the powertransmittance directly toward the food load through the abuse-tolerantmetallic segments 808 is dramatically decreased, which leads to aquasi-shielding functionality. In the absence of food contacting theabuse-tolerant packaging material 800, the array effect of the smallmetallic segments 808 still maintains a generally transparentcharacteristic with respect to microwave power energy. Thus, the chancesof arcing or burning when the material is unloaded or improperly loadedare diminished.

Preferably, each of the metallic segments 808 has an area less than 5mm² and the gap between each of the small metallic segments 808 islarger than 1 mm. Metallic segments 808 of such size and arrangementreduce the threat of arcing that exists under no-load conditions inaverage microwave ovens. When, for example, food, a glass tray, or alayer of plain susceptor film 805 contacts the metallic segments 808,the capacitance between adjacent metallic segments 808 will be raised aseach of these substances has a dielectric constant much larger than atypical substrate on which the small metal segments 808 are located. Ofthese materials, food has the highest dielectric constant (often by anorder of magnitude). This creates a continuity effect of connectedmetallic segments 808, which then work as a low Q-factor resonate loop,power transmission line, or power reflection sheet with the samefunction of many designs that would otherwise be unable to withstandabuse conditions. On the other hand, the pattern is detuned from theresonant characteristic in the absence of food. This selectively tunedeffect substantially equalizes the heating capability over a fairlylarge packaging material surface including areas with and without food.

The perimeter of each set of metallic segments 808 is preferably apredetermined fraction of the effective wavelength of microwaves in anoperating microwave oven. The predetermined fraction is selected basedon the properties of the food to be cooked, including the dielectricconstant of the food and the amount of bulk heating desired for theintended food. For example, a perimeter of a set of metallic segments808 can be selected to be equal to predetermined fractions or multiplesof the effective microwave wavelength for a particular food product.Furthermore, a resonant fraction or multiple of the microwave wavelengthis selected when the abuse-tolerant microwave packaging material 800 isto be used to cook a food requiring strong heating, and a smaller,high-density, nested perimeter of a quasi-resonant, fractionalwavelength is selected when the abuse-tolerant microwave packagingmaterial 800 is used to cook food requiring less heating, but moreshielding. Therefore, the benefit of concentric but slightly dissimilarperimeters is to provide good overall cooking performance across agreater range of food properties (e.g., from frozen to thawed foodproducts).

The embodiment depicted in FIGS. 9A, 9B, and 9C is a combination of thestructures of the embodiments of FIGS. 4 and 5. It has been found thatwhen the insulating microwave packaging material is made in the form ofa bag or pouch, the cells generally expand more uniformly. In thisembodiment a sealed pouch 900 is formed by bringing two opposing edgesof a first sheet of insulating microwave packaging material 940 togetherwith the top surface 920 (FIG. 9C) composed of the susceptor layerfacing inward and the bottom surface 922 composed of the second plasticfilm facing outward. The two opposing edges of the first sheet ofpackaging material 940 are fastened together, for example, via heatsealing or adhesive, to form a sealed edge 924 a. The first sheet ofpackaging material 940 is thereby transformed into an envelope or sleeveinto which a food product 930 may be placed. Alternatively, the firstsheet 940 could be wrapped around the food product 930 with the foodproduct 930 in situ. Next, the opposing edges of the first sheet 940 ateach open end of the sleeve are also fastened together, again forexample, via heat sealing or adhesive, to form sealed edges 924 b and924 c, respectively, forming a completely sealed pouch 900. The cornersof the sealed pouch 900 are then cut off to provide vent holes 926 a,926 b, 926 c, and 926 d that allow steam from the food product 930 toescape.

During the manufacture of the pouch 900, a second sheet of insulatingmicrowave packaging material 950 is attached to the bottom side 952 ofthe pouch 900, i.e., the side of the pouch 900 that will rest on thefloor or turntable of a microwave oven during cooking. The secondplastic film side of the second sheet 950 faces the second plastic filmside of the first sheet 940. The second sheet 950 may be tacked to thefirst sheet 940, for example, by adhesive or heat seal, at severalpoints 956 spaced apart from each other along the perimeter of thesecond sheet 950. For example, if the second sheet 950 is square orrectangular, the corners of the second sheet 950 may be tacked to theouter surface of the first sheet 940. The second sheet of packagingmaterial 950 is only attached at points 956 at the corners to allow formovement of the second sheet 950 in the X and Y directions.

In this embodiment, as the susceptor film in the first sheet 940 heats,the pouch 900 expands to form the pillows on the top surface 920, whichbring the susceptor film in close proximity to or contact with the foodproduct 930 on all sides, providing the desired cooking effect on allsides of the food product 930. The channels between the pillows in thequilted top surface 920 provide the added benefit of venting water vaporreleased from the food product 930 to the vent holes 926 a, 926 b, 926c, 926 d during cooking, which further enhances the surface browning andcrisping effects of the susceptor film. The vapor filled cells of thefirst sheet 940 also further insulate the food product 930 from themicrowave oven environment and ensure the heat generated remains in thefood product 930 rather than transferring to the oven environment.

As discussed above, a frozen food product placed upon a microwave ovensurface will cool the microwave oven surface before the microwave ovenis energized, increasing the amount of heat transfer to the microwaveoven surface once the cooking process begins. In the embodiments ofFIGS. 9A, 9B, and 9C, similar to the embodiment of FIG. 5, the secondsheet 950 of microwave packaging material intercedes between the firstsheet 940 and the microwave oven floor to insulate the bottom side 952of the pouch 900 from the microwave oven floor. The susceptor film ofthe second sheet 950 heats the microwave oven surface and forms pocketsof water vapor in its cells 954 creating a pillowed surface 958 thatinsulates the first sheet 940 of the pouch 900 from the floor of themicrowave oven. This allows the heat of the susceptor film of the firstsheet 940 to be concentrated on the food product 930, counteracting theability of the microwave oven floor to act as a heat sink. Further, inthe case of a frozen or cold food product, the second sheet 950 createsenough heat energy immediately to cause vapor expansion in the cells 914of the first sheet 940 of the microwave packaging material soon afterthe microwave oven is energized. If the second sheet 950 of microwavepackaging material were not present, the frozen food product wouldsignificantly increase the time required to heat the water vapor and airand achieve expansion of the cells 914 in the first sheet 940 becausethe surface temperature of the susceptor film of the first sheet 940 onthe bottom side 952 of the pouch 900 will not rise until the surfacetemperature of the food product accordingly rises.

Alternatively, the sealed pouch may be formed of a sheet of a regularsusceptor material, for example, MicroFlex®Q, that does not expand likethe first sheet 940 to provide insulation. In this example, the secondsheet of insulating microwave packaging material 950 described above isstill attached to the bottom side of the pouch. In this manner, thesecond sheet 950 will still expand to insulate the pouch of susceptormaterial from the microwave oven floor and improve the cookingperformance of the susceptor material against the food product 930.

Cool-to-the-Touch Microwave Packaging Materials

In a further embodiment of the invention, the quilting effect is createdin a layer of polyester film separated from the susceptor film. Not onlyis the microwave packaging insulated from the vented air of themicrowave oven, the quilted layer also protects a consumer from theresidual heat of the susceptor film after cooking. As shown in FIG. 10A,an insulating microwave packaging material 1000 is composed of severalsubstrate layers. The top layer is a first plastic film 1010, preferablyan amorphous polyester film, that is adhered to a dimensionally stablesubstrate, in this instance paperboard 1008. The plastic film 1010 isbonded in a patterned manner, wherein bond lines of adhesive 1012 forman array of very small closed cells 1014 between the plastic film 1010and the paperboard 1008. In this embodiment, the area of the cells 1014may be on the order of 0.625 in² and 0.125 in². The opposite side of thepaperboard 1008 is adhered to a susceptor film 1005 by a layer ofadhesive 1006. The susceptor film 1005, as in previous embodiments, maybe a second plastic film 1002, for example, polyester, coated with athin layer of metal 1004, for example, aluminum.

Upon impingement by microwave energy, the insulating microwave packagingmaterial 1000 undergoes a transformation as shown in FIG. 10B. As thesusceptor film 1005 heats, some of the heat is transferred through thepaperboard 1008 to the first plastic film, which softens.Simultaneously, moisture trapped in the paperboard 1008 heats andexpands as gaseous water vapor into the cells 1014. Unlike thebiaxially-oriented polyester of the previous embodiments, the firstplastic film 1010, of amorphous polyester or other plastic with similarcharacteristics in this embodiment, does not contract when heated andinstead puffs out under the pressure of the expanding water vapor as itsoftens to form tiny pillows 1016 across the top surface 1020 of theinsulating microwave packaging material 1000.

Although the paperboard 1008 is thicker, and thereby more insulatingthan the paper layers of previous embodiments, the amorphous polyesterfilm 1010 has a lower heat distortion temperature than thebiaxially-oriented polyester of the previous embodiments. Therefore, theamorphous polyester film 1010 will soften and yield to the pressure ofexpanding water vapor at a lower temperature. Thus, the quilting effectin the first plastic film 1010 is achieved at a lower surfacetemperature of the top surface 1020 than in previous embodiments becausethe necessary heat transfer through the paperboard 1008 is reduced.

The combination of quilting and lower surface temperature may provideseveral consumer benefits. As depicted in FIG. 10C, a microwave cookingcontainer 1025 is constructed of the insulating microwave packagingmaterial 1000 of FIG. 10A. The susceptor film 1005 lines the interior ofthe container 1025 to contact the food to be cooked within. Thestructure of the container 1025 is provided by the sturdy paperboard1008 layer. FIG. 10C depicts the container 1025 after exposure tomicrowave energy. The exterior surface 1020 of the container 1025 iscovered by an array of pillowed cells 1016. Not only do the pillowedcells 1016 provide insulation for the container 1025 from the microwavecooking environment during cooking, the pillows 1016 further provideinsulation against heat transfer from the susceptor film 1005 to theconsumer upon contacting the container 1025 to remove it from themicrowave oven or otherwise hold the container 1025 during consumptionof a food product contained therein.

A further embodiment of the invention that provides insulation againstheat transfer to the consumer, shown in FIGS. 11A and 11B, uses thetechnology described above to make portions of the susceptor inactive.FIG. 11A depicts a sheet 1100 of insulating microwave interactivematerial according to the present invention. The desired adhesivepattern 1112 is shown outlining the perimeter of the sheet 1100 andoutlining the cells 1114 as well. In this embodiment, each of the cells1114 is an elongated rectangle that, when heated, will form a tube-likepouch. FIG. 11B indicates the inactive areas 1106 of the sheet 1100 thatwill not heat upon impingement by microwave energy. However, the cells1114 still include a microwave energy interactive layer 1105 in order toheat the surface of a food item and expand the cells 1114 into a pillowform.

FIGS. 12A and 12B show a sheet 1200 of insulating microwave interactivematerial with an alternate cell 1214 design. In this design, the cells1214 are elongate diamond shapes. The pointed ends of each cell 1214allow the pouch structure formed upon heating to contract around thefood item more uniformly relative to the purely box ended cells 1114 ofFIGS. 11A and 11B. The adhesive pattern 1212 is again shown in FIG. 12Aoutlining the perimeter of the sheet 1200 and outlining the cells 1214.Likewise, FIG. 12B indicates the inactive areas 1206 of the sheet 1200that will not heat upon impingement by microwave energy. Again, thecells 1214 still include a microwave energy interactive layer 1205 inorder to heat the surface of a food item and expand the cells 1214 intoa pillow form.

Because the sheets 1100, 1200 of insulating microwave interactivematerial are inactive along the adhesive patterns 1112, 1212 outliningthe cells 1114, 1214, the areas of the adhesive patterns will not heatduring microwave cooking. This effect provides an opportunity to designmicrowave packaging products with exterior surfaces cool to the touchfor a consumer. One example of such a packaging design is shown in FIGS.13A-13D.

FIG. 13A depicts a cooking pouch 1350 formed by folding a sheet 1300 ofinsulating microwave interactive material as shown in FIGS. 12A and 12Bto bring two opposite ends together. The opposing ends may be sealed asa seam 1324 a to form a sleeve. One of the open ends of the sleeve isthen further sealed forming a seam 1324 b to close the end of the sleeveand form a pocket with an opening along the opposing side. The edgeseams 1324 a and 1324 b may be adhered together with adhesive or heatsealed as previously described herein. When the cooking pouch 1350 isreceives incident microwave energy in a microwave oven, the susceptorareas 1305 forming part of the walls of the cells 1314 heat and causethe air and water vapor in the cells 1314 to expand and form elongateinsulating elongate pillows 1316 within the cooking pouch 1350 as shownin FIGS. 13B and 13D.

FIG. 13C shows in exaggerated detail the how the elongate pillows 1316are formed upon the heating of the cells 1314 by the active portion ofthe susceptor 1305 of the packaging material 1300. Although in actualitythe sheet of packaging material 1300 is a single sheet wrapping over andunder the food item 1330, for convenience of reference the portionspositioned on top of the food item 1330 are denoted with an “a” and thelike portions positioned on the bottom of the food item 1330 are denotedwith a “b.” Therefore, sheet 1300 a on top of the food item 1330 ismirrored by sheet 1300 b below the food item. The outer layers of sheets1300 a and 1300 b are composed of a plastic film layer 1310 a, 1310 bthat upon heating becomes separated from the remaining layers of thesheets 1300 a, 1300 b by the expansion of air and water vapor. The edgesof the plastic film layers 1310 a, 1310 b are adhered to the edges ofrespective dimensionally stable paper substrate layers 1308 a, 1308 b byadhesive patterns 1312. The sides of the paper layers 1308 a, 1308 bopposite the plastic film layers 1310 a, 1310 b are adhered to susceptorfilm layers 1305 a, 1305 b by respective comprehensive layers ofadhesive 1306 a, 1306 b. The susceptor film layers 1305 a, 1305 b are asbefore composed of a layer of plastic film 1302 a, 1302 b coated with athin, microwave interactive layer of aluminum 1304 a, 1304 b. In thisembodiment, portions 1340 of the aluminum layers 1304 a, 1304 b havebeen inactivated from heating by microwave energy to providecool-to-touch areas and to aid in maintaining the edge seal 1324 b.

On the exterior surface of the cooking pouch 1350, raised ribs 1340 areformed, as shown in FIGS. 13B and 13D, in the same pattern as theadhesive pattern 1312 due to the pillowing of the susceptor layer andthe contraction of the outer plastic film layer forming the insulatingmicrowave interactive material sheet 1300. These raised ribs 1340 arecool to the touch because they conform to the inactive areas 1306 of thesusceptor and therefore were not substantially heated during the cookingprocess. In this manner a microwave cooking package is created that maybe grasped and held by a user immediately after microwave heatingwithout burning the user's hands.

One embodiment of the invention may include the use of the insulatingmicrowave packaging material of the present invention in conjunctionwith commercially available fast food packaging designs. FIGS. 14A and14B depict one such potential package combination 1410. As in the priorcommercial designs (developed by Rapid Action Packaging, United Kingdom;further described in U.S. Pat. Nos. 5,921,681; 6,016,950; 6,335,042; and6,431,365), a folding carton blank 1450 with a front panel 1452 andaback panel 1454 is combined with a flexible pouch 1400 to form thepackage 1410. Opposing panels of the pouch 1400 are adhered to both thefront panel 1452 and the back panel 1454 of the folding carton blank1450. The folding carton blank 1450 folds in half along score line 1456or perforation and further features an arcuate score 1458 or perforationon each of the front panel 1452 and the back panel 1454. The bottomscore line fold 1456 allows the carton blank 1450 to fold flat for easyshipping and storage before filling with a food item 1430. The arcuatescore lines 1458 provide a snap-open design with an arcuate bottom panel1460. When the user moves the front panel 1452 apart from the back panel1454, the carton 1450 snaps open the flexible pouch 1400 in a bowl-likeconfiguration to receive a food item 1430. After the food item 1430 isplaced in the carton 1450, the open end of the flexible pouch 1400 maybe sealed or merely folded over and tucked to close the carton 1450around the food item 1430 securely.

The flexible pouch 1400 may be constructed of the insulating microwavepackaging material of the present invention, or alternately othernon-insulating susceptor materials, for example, MicroFlex®Q orMicroRite®. Such susceptor materials are preferably heat sealable sothat the edges 1424 may be sealed together to form the pouch 1400. Thepanel edges of the pouch 1400 may alternatively be held together withadhesive. (In the prior art design, the flexible pouch is composed ofpolyethylene coated paper or clear polymer film, which is heatsealable.) Patterned microwave active and passive areas may be etchedinto the susceptor material using the techniques previously describedherein. The active areas in the location of the cells 1414 provide thelofting effect to the cells 1414. The passive areas provide for strongerpouch seals 1424 and help in the formation of surfaces, for example,raised ribs 1440, as finger holds, which are cool to the touch.

One useful examples for such a combination package 1410 is for a masterpack, including multiple carton 1450 and pouch 1400 combinationsaccording to this invention, and a package of finger style food items,e.g., French fries. The consumer may open the master pack and select anindividual package 1410 formed according to this invention, pop open thebottom of the carton 1460, thereby opening the pouch 1400, fill thepouch 1400 with a serving of food, fold over the pouch opening and placethe package in the microwave oven. After heating the consumer may reachinto the microwave oven and grab the package by hand. The microwaveinactive portions 1440 of the pouch 1400 and the carton 1450 itself arecool-to-the-touch. In this manner, the user may, unfold the pouch 1400immediately to form the bowl-like shape and consume the food item 1430.Further, the design carton blank 1450 with the arcuate bottom panel 1460separates the pouch 1400 completely from heat sink contact with themicrowave oven floor, resulting in superior cooking performance of themicrowave active pouch 1400.

The package 1410 of this invention can also be executed as a consumerretail package. A food processor would form a microwave active pouch1400 from roll stock, attach the pouch 1400 to the paperboard cartonblank 1450 with glue, fill the pouch 1400, and heat seal the pouch 1400closed. The pouch 1400 and carton blank 1450 may be printed withgraphics, which promote the product and instruct the consumer in the useof the package 1410. The package 1410 may be sized, for example, to fitin a cup holder facilitating eat-on-the-go convenience store sales. Thepackage 1410 could be distributed either with the carton bottom 1460erected open or folded flat. If folded flat, the consumer would beinstructed to pop the carton bottom open 1460 and place the package 1410with the food item 1430 in a microwave oven for heating. After removingthe package 1410 from the microwave oven, the pouch seal is peeledopened at a cool-to-the-touch finger hold area 1440, which is microwaveinactive.

Either cold glue or cold glue in combination with hot melt may be usedto attach the microwave active pouch 1400 to the carton blank 1450. Hotmelts bond quickly compared to cold glues, and thus increase packagefabrication speeds. However, hot melts may react at the temperaturesreached by the susceptor pouch 1400, allowing the pouch to detach fromthe carton blank 1450 and fall to the oven floor defeating the packagedesign function. Cold glues on the other hand may be selected to resisttemperatures above those reached by the microwave susceptor pouch 1400,avoiding this problem. Alternatively, the hot melt could be placed incorresponding position relative to a microwave susceptor inactive area1440, also circumventing this problem.

Pouches constructed of two sheets of insulating microwave interactivematerial as used in several of the previous embodiments may take onvarious forms and shapes. One example depicted in FIGS. 15A-15D is apouch formed as a right trapezoid designed to hold a triangular-shapedfood item 1530, for example, a slice of pizza FIG. 15A depicts a sheet1500 of insulating microwave interactive material according to thepresent invention. The desired adhesive pattern 1512 is shown outliningthe perimeter of the sheet 1500 and outlining the cells 1514 as well. Inthis embodiment, each of the cells 1514 is a triangle that, when heated,will form an insulating pouch 1516 (see FIG. 15D). FIG. 15B indicatesthe inactive areas 1506 of the sheet 1500 that will not heat uponimpingement by microwave energy. However, the cells 1514 still include amicrowave energy interactive layer 1505 in order to heat the surface ofa food item and expand the cells 1514 into a pillow form.

FIG. 15C depicts a cooking pouch 1510 formed by adhering two sheets 1500a, 1500 b of insulating microwave interactive material together aroundthree perimeter edges 1524 a, 1524 b, 1524 c to form a pocket with anopening at the wider parallel side. The edges 1524 a, 1524 b, 1524 c maybe adhered with adhesive or heat sealed as previously described herein.When the cooking pouch 1510 receives incident microwave energy in amicrowave oven, the susceptor areas 1505 forming part of the walls ofthe cells 1514 heat and cause the air and water vapor in the cells 1514to expand and form elongate insulating pillows 1516 within the cookingpouch 1510 as shown in FIG. 15D. On the exterior surface of the cookingpouch 1510, raised ribs 1540 are formed in the same pattern as theadhesive pattern 1512 due to the pillowing of the susceptor layer andthe contraction of the outer plastic film layer forming the insulatingmicrowave interactive material sheets 1500 a, 1500 b. These raised ribs1540 are cool to the touch because they conform to the inactive areas1506 of the susceptor and therefore were not substantially heated duringthe cooking process.

Another embodiment of the invention for providing low heat transferpackaging surfaces oriented toward the consumer is depicted in FIG. 16.A microwavable package 1600 is provided in the form of a modifiedmicrowave cooking sleeve. A microwave cooking sleeve is generally apaperboard sleeve that surrounds a food product. A microwave interactivelayer, for example, susceptor film (e.g., MicroFlex®Q or MicroRite®) orthe quilted susceptor of the present invention, is generally laminatedor otherwise attached to the interior wall of the paperboard sleeve. Thesusceptor film is used to brown and crisp the exterior of the foodproduct placed within the microwave cooking sleeve.

The microwavable package 1600 of FIG. 16 is actually formed more like apocket than a sleeve. A paperboard outer wall 1602 lined on the interiorsurface with a susceptor film 1604 surrounds the food product 1620. Themicrowavable package is further constructed to form a base 1606, whichmay be used to stand the microwavable package 1600 upright for display,storage, cooking, and resting during eating. The base 1606 may merely bean extension of the paperboard outer wall 1602. Concealed within thepaperboard outer wall 1602 and situated above the base 1606 is a floor1610 that supports the food product 1620 when the microwavable package1600 is placed upright on the base 1606. The floor 1610 keeps the foodproduct 1620 spaced apart from a surface upon which the base 1606 of themicrowavable package 1600 may rest. The floor 1610 may be a paperboardpanel adhered to the interior surface of the paperboard outer wall 1602,similar to the construction of certain paper cups.

Provided within the base 1606 at one or more locations are vent windows1608. These base vent windows 1608 may be cutouts along the bottom edgeof the base 1606 as depicted in FIG. 16, or they may be apertures fullysurrounded by the surface area of the base 1606. Further, within thefloor 1610 are one or more floor vent holes 1612, provided to cooperatewith the base vent windows 1608 to allow air flow into the area of themicrowavable package 1600 housing the food product 1620.

The microwavable package 1600 is open at the top like a chimney 1616 toallow water vapor released by the food product 1620 during cooking toescape the constraints of the microwavable package 1600. The reductionof water vapor in the microwavable package 1600 increases the browningand crisping effect of the susceptor film 1604 on the food product, asotherwise the water vapor would counteract the drying effect of thesusceptor film 1604. The top edge or rim of the paperboard outer wall1602 may be folded, either outward or inward (as shown in FIG. 16), toform a lip 1614 surrounding the chimney opening 1616. This lip 1614 maybe used as a support for a package seal that protects the food product1620 before consumer use and that may be easily removed by the consumerbefore cooking and eating the food product 1620. A simple paper orplastic sheet adhered to the lip 1614 and pulled off by the consumer maysuffice.

As the heated water vapor rises and exhausts through the chimney opening1616, a draft is created in conjunction with the floor vent holes 1612and the base vent windows 1608 whereby relatively drier outside air isdrawn through the microwavable package 1600 and across the food product1620. The overall exterior shape of the microwavable package 1600 maytaper from bottom to top to enhance the chimney effect. The drafting airflow helps with the removal of water vapor as the unsaturated dry air isable to absorb additional water vapor. This increases the crisping andbrowning effect of the susceptor film 1604 on the food product 1620. Thedrafting air further provides some convection within the microwavablepackage 1600, thereby distributing the heat within the package andproviding a more uniform cooking result.

Another embodiment of a microwavable package 1700 is depicted in FIG.17. In this embodiment, a top cup 1702 is inverted and placed upon abottom cup 1704 such that the major openings of each cup 1702, 1704 areadjacent to each other. Together the top cup 1702 and the bottom cup1704 form a canister that encapsulates a food product 1720. The top cup1702 may be provided with a first lip 1706 along the rim defining themajor opening of the top cup 1702, and the bottom cup 1704 may beprovided with a second lip 1708 along the rim defining the major openingof the bottom cup 1704. The lips 1706, 1708 are preferably foldedoutwardly, away from the outer surface of the cups 1702, 1704, therebyallowing the top cup 1702 to nest or stack within the bottom cup 1704(or vice versa) for ease of storage and reduced shipping bulk before thecups 1702, 1704 are formed as a canister to surround a food product1720. Use of the cup shape also provides convenience to the consumer,for example, for holding the microwavable package 1700 while eating thefood product 1720, standing the microwavable package 1700 upright forstorage or during cooking, or eating on-the-go, as the microwavablepackage 1700 will easily rest in an automobile cup holder.

Each of the top cup 1702 and bottom cup 1704 may be constructed ofpaperboard and lined on its interior surface with a susceptor, as in theembodiment shown in FIG. 16. Further, the bottom cup 1704 may includevent windows 1714 in its base 1716, and similarly vent holes (not shownin FIG. 17, but substantially the same as the vent holes 1612 in FIG.16) in the floor 1718 of the cup. The top cup 1702 maybe made exactlythe same as the bottom cup 1704 with vent windows 1715 in the base 1717and vent holes (not shown) in its inverted floor 1719. The vent holes inthe top cup 1702 may perform the same function as the chimney opening1616 in the microwavable package 1600 of FIG. 16 by allowing the watervapor generated during cooking to exhaust and creating an air flow drawin conjunction with the vent windows 1714 and vent holes of the bottomcup 1704. The vent windows of the top cup 1702 are nonfunctional in thisinstance. However, by this symmetric design, the top cup 1702 can besubstituted for the bottom cup 1704 during assembly of the canisterarrangement, making the manufacture of only one form of a cup necessary.Further, the floor 1719 of the top cup 1702 (and similarly the floor1718 of the bottom cup 1704) may be made to be easily removable by theconsumer to create a large, chimney-like opening in the top cup 1702 asin the embodiment of FIG. 16.

The top cup 1702 may be sealed to the bottom cup 1704 by adhering thelips 1706, 1708 of the cups together. As an alternative example, plasticshrink-wrap tear-tape 1710 may be used to hold the top cup 1702 andbottom cup 1704 together at the interface between the lips 1706, 1708.The use of tear-tape 1710 further provides tamper evidence to theconsumer to assure the safety of the food product 1720. With the use oftear-tape 1710, the consumer may quickly open the microwavable package1700 by pulling the tear-tape 1710 and lifting the top cup 1702 off thebottom cup 1704, revealing the food product contained with Alternately,plastic shrink-wrap may cover the entire microwavable package 1700, forexample, for freezer protection. A tear-strip 1710 may be placed in aportion of the shrink wrap to facilitate opening of the microwavablepackage 1700. The shrink-wrap may also be printed with graphics andother product information to minimize the cost of manufacture of themicrowavable package 1700. The consumer may further proceed to eat thefood product while holding the bottom cup 1704 in hand. In this manner,the microwavable package 1700 becomes a convenient, portable, on-the-go,serving utensil.

To aid in the ability of the bottom cup 1704 to be used as a servingutensil, a corrugated paper sleeve 1712, or other insulating surface maybe placed on the outer surface of the bottom cup 1704 to insulate theconsumer's hand from the extreme heat of the susceptor film transferredthrough the paperboard wall of the bottom cup 1704. Other materials maybe used to provide the desired consumer insulation on the outer surfaceof the bottom cup 1704. These materials may include, for example, acavitated film coating; a high density polyethylene coating, apolyvinyl-chloride shrink-wrap sleeve; and the polypropylene substrateconfiguration that creates the quilted, air-cell surface as shown anddescribed herein with respect to FIG. 10C.

Another embodiment of a microwavable package 1800 according to thepresent invention is depicted in FIG. 18. The microwavable package 1800is of a similar configuration to the microwavable package 1700 of FIG.17. The microwavable package 1800 consists of a top cup 1802 invertedand placed upon a bottom cup 1804 such that the major openings of eachcup 1802, 1804 are adjacent to each other. Together the top cup 1802 andthe bottom cup 1804 form a canister that encapsulates a food product1820. The outer wall 1806 of the top cup 1802 and the outer wall 1808 ofthe bottom cup 1804 may each be constructed of paperboard and lined oneach respective interior surface with a susceptor 1810, 1812. Further,the bottom cup 1804 may include vent windows in its base and vent holesin a floor (not shown), similar to the corresponding structures depictedin and described with respect to FIGS. 16 and 17. The top cup 1802 mayalso include some type of venting aperture in its inverted floor 1803 asdescribed with respect to FIG. 17, or the floor panel 1803 may bedesigned to be easily removed by the consumer for cooking, as describedwith respect to FIG. 16.

The top cup 1802 has a rim 1814 defining the major opening of the topcup 1802. The bottom cup 1804 maybe formed with a flange 1816 along itsrim 1815 defining the major opening of the bottom cup 1804. The flange1816 may be formed in the rim 1815 of the bottom cup 1804 by compressionof the paperboard forming the bottom cup 1804, for example, in a mold ora clamping device. The flange 1816 may extend beyond the outer surfaceof the bottom cup 1804 to form a shelf 1818 along the rim 1815. Themajor opening in the top cup 1802 defined by the rim 1814 and the majoropening in the bottom cup 1804 defined by the rim 1815 may besymmetrical in dimension such that the rim 1814 of the top cup 1802rests upon the shelf 1818. The flange 1816 of the bottom cup 1804extends above the shelf 1818 and covers a portion of the exteriorsurface of the top cup 1802 along its rim 1814. In this manner, the topcup 1802 nests within the flange 1816 of the bottom cup 1804 to form acanister. As with the second embodiment described with respect to FIG.17, the bottom cup 1804 may be covered with an insulating surface (notshown) to mitigate heat transfer to the consumer when holding themicrowavable package 1800 after it has been heated in a microwave oven.

In the embodiment of FIG. 19, a microwavable package 1900 is againformed from a paperboard substrate. The upper portion 1902 of themicrowavable package 1900 contains the food product 1920 to be heated.The inner wall of the paperboard substrate in the upper portion 1902 maybe covered by a susceptor (not shown) to enhance the crisping andbrowning of the food product 1920 inside. The food product 1920 may besupported by a floor 1906 in the upper portion 1902 of the microwavablepackage 1900 that separates the upper portion 1902 from the lowerportion 1904.

The lower portion 1904 of the microwavable package 1900 may not becovered by a susceptor film as there is no food product 1920 in lowerportion of the microwavable package 1900. Further, the lower portion1904 may be tapered for ease of holding the microwavable package 1900 bythe consumer. For example, if the upper portion 1902 of the microwavablepackage 1900 were cylindrical, as the cup embodiments previouslydescribed, the lower portion 1904 may be a frustum. The bottom 1910 ofthe lower portion 1904 may be flat in order to support the microwavablepackage 1900 in an upright position on a flat surface, for example, on ashelf for storage or in the microwave during cooking.

As in the previous embodiments described with respect to FIGS. 16-18,the microwavable package 1900 depicted in FIG. 19 may provide for upwardexhausting of water vapor from the upper portion during cooking. The top1908 of the upper portion 1902 may be a sheet, for example of paper orplastic, that is easily removable by the consumer. Alternatively, thetop 1908 may contain apertures to allow the water vapor released duringthe cooking process to escape the upper portion 1902. In addition, thefloor 1906, in conjunction with the lower portion 1904, may beconfigured to provide a draft through vent holes (not shown) in thefloor 1906 and vent windows 1912 in the lower portion 1904, creating achimney effect as described with respect to previous embodiments.

Yet another embodiment of the present invention is depicted in FIG. 20.A microwavable package 2000 is created from a paperboard substrateforming a package wall 2002. Lining the interior of the package wall2002 is a corrugated susceptor 2004 (i.e., a susceptor film adhered to adimensionally stable substrate, for example, paper). The corrugatedsusceptor 2004 provides enhanced browning and crisping to a food product2020 placed within the microwavable package 2000. The corrugatedsusceptor 2004 provides an added benefit by mitigating the heat transferbetween the corrugated susceptor 2004 and the package wall 2002, andthus heat transfer to the consumer holding the microwavable package 2000after cooking. This mitigation occurs because of the low surface areacontact between the corrugated susceptor 2004 and the package wall 2002.

When used in a package configuration as depicted in FIG. 16, thecorrugated susceptor 2004 of FIG. 20 provides additional benefits. Ifthe food product 2020 is bulky or substantially fills the space withinthe microwavable package 2000, the corrugated susceptor 2004 may stillprovide for venting of water vapor from the food product 2020 along thechannels forming the corrugation. Similarly, a draft of air from ventsin the bottom of the microwavable package 2000 may still be drawn tocreate a chimney-like effect with an opening in the top of themicrowavable package 2000. Further, the channels formed between thecorrugated susceptor 2004 and the package wall 2002 may allow air todraft from vents in the bottom of the microwavable package 2000, whichfurther insulates the package wall 2002 from the heat of the corrugatedsusceptor 2004.

Although various embodiments of this invention have been described abovewith a certain degree of particularity, or with reference to one or moreindividual embodiments, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thespirit or scope of this invention. It is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative only of particularembodiments and not limiting. Changes in detail or structure may be madewithout departing from the basic elements of the invention as defined inthe following claims.

1. A microwavable baking surface comprising: a baking substratecontaining an aperture; a first sheet of an insulating microwavepackaging material; and a second sheet of the insulating microwavepackaging material; wherein the first sheet and the second sheet arearranged adjacent to each other and substantially cover the aperture,the insulating microwave packaging material includes a layer ofmicrowave energy interactive material supported on a first polymer film,a dimensionally stable substrate joined to the layer of microwave energyinteractive material, and a second polymer film joined to thedimensionally stable substrate in a patterned configuration that definesa plurality of closed cells between the dimensionally stable substrateand the second polymer film, and upon sufficient exposure to microwaveenergy, at least some of the closed cells inflate, and the first polymerfilm, the layer of microwave energy interactive material, and thedimensionally stable substrate bulge away from the second polymer film.2. The microwavable baking surface of claim 1, wherein the first sheetis adapted to receive a food item for heating, and the inflated closedcells of the second sheet reduce heat loss from at least one of the fooditem and the first sheet.
 3. The microwavable baking surface of claim 1,wherein the second polymer film of the first sheet faces the secondpolymer film of the second sheet.
 4. The microwavable baking surface ofclaim 1, wherein the baking substrate includes a upper surface and alower surface, the first sheet and the second sheet each have aperipheral region, at least a portion of the peripheral region of thesecond polymer film of the first sheet is joined to the upper surface ofthe baking substrate, and at least a portion of the peripheral region ofthe second polymer film of the second sheet is joined to the lowersurface of the baking substrate.
 5. The microwavable baking surface ofclaim 4, wherein at least one of the first sheet and the second sheet isjoined to the baking substrate using an adhesive that softens inresponse to temperature.
 6. The microwavable baking surface of claim 1,wherein upon impingement of the insulating microwave packaging materialby microwave energy, the first sheet deforms into a convex canopy withrespect to a plane dividing the first sheet and the second sheet, and aspace is created between the first sheet and the second sheet.
 7. Themicrowavable baking surface of claim 1, wherein upon impingement of theinsulating microwave packaging material by microwave energy, the secondsheet deforms into a convex canopy with respect to a plane dividing thefirst sheet and the second sheet, and a space is created between thefirst sheet and the second sheet. space is created between the firstsheet and the second sheet.
 8. The microwavable baking surface of claim1, wherein the baking substrate comprises paperboard.
 9. Themicrowavable baking surface of claim 1, wherein the baking substratecomprises a susceptor.
 10. The microwavable baking surface of claim 1,wherein the baking substrate comprises an abuse-tolerant microwavepackaging material.
 11. The microwavable baking surface of claim 1,wherein the baking substrate is disk-shaped.
 12. The microwavable bakingsurface of claim 11, wherein the aperture is circular and concentricwith the baking surface.
 13. A microwave cooking container comprising: abody formed from a dimensionally stable material, the body including atleast one wall at least partially covered by a microwave energyinteractive material, a floor adapted to support a food item, and anopening opposite the floor; and a base adapted to support the body, thebase including a venting aperture.
 14. The microwave cooking containerof claim 13, wherein the microwave energy interactive material issupported on a polymer film, and the polymer film defines at least aportion of an interior surface of the body.
 15. The microwave cookingcontainer of claim 13, wherein the microwave energy interactive materialis supported on a first polymer film, a moisture-containing substrate isjoined to the microwave energy interactive material, and a secondpolymer film is joined to the moisture-containing substrate in apatterned configuration that defines a plurality of expandableinsulating cells.
 16. The microwave cooking container of claim 15,wherein upon sufficient exposure to microwave energy, at least somecells of the plurality of expandable insulating cells inflate.
 17. Themicrowave cooking container of claim 13, wherein the body includes aninterior surface and an exterior surface opposite the interior surface,and the exterior surface comprises a thermal insulating material. 18.The microwave cooking container of claim 13, wherein the body comprisesan upper portion and a lower portion, and the upper portion and thelower portion are each of separate construction, and the upper portionis attached to the lower portion at a common interface between the upperportion and the lower portion.
 19. The microwave cooking container ofclaim 18, wherein the upper portion and the lower portion each includean interior surface, and the interior surface of at least one of theupper portion and the lower portion is corrugated.
 20. The microwavecooking container of claim 18, wherein the upper portion and the lowerportion each independently include a major opening having a rim, and theupper portion and the lower portion are arranged in an opposedrelationship such that the respective major openings of the upperportion and the lower portion cup are adjacent and open to one other.21. The microwave cooking container of claim 20, wherein the respectiverims of the first cup and the second cup each independently comprise alip extending outwardly from the exterior surface thereof, and therespective rims are aligned substantially and in contact with eachother.
 22. The microwave cooking container of claim 20, wherein theupper portion and the lower portion each independently include an enddistal to the major opening, and the upper portion and the lower portionare capable of being stacked in a nested configuration with therespective major openings adjacent to one another and the respectiveends being adjacent one another.
 23. A microwavable package for heatinga food item, the package comprising: a canister having an interiorsurface, an exterior surface, and a cavity capable of receiving a fooditem, at least a portion of the interior surface including a microwaveenergy interactive material, wherein the canister comprises a first cupand a second cup, the first cup and the second cup each independentlyincluding a major opening having a rim, the first cup and the second cupbeing arranged in an opposed relationship such that the respective majoropenings of the first cup and the second cup are adjacent and open toone other.
 24. The microwavable package of claim 23, wherein therespective rims of the first cup and the second cup are alignedsubstantially and in contact with each other.
 25. The microwavablepackage of claim 23, wherein the rim of at least one of the first cupand the second cup comprises a lip extending outwardly from the exteriorsurface thereof.
 26. The microwavable package of claim 23, wherein therespective rims of the first cup and the second cup each independentlycomprise a lip extending outwardly from the exterior surface thereof,and the respective rims are aligned substantially and in contact witheach other.
 27. The microwavable package of claim 23, wherein the rim ofthe first cup comprises a flange including a shelf, and the rim of thesecond cup is aligned with the shelf of the first cup.
 28. Themicrowavable package of claim 23, wherein the respective rims of thefirst cup and the second cup are joined separably by an adhesive. 29.The microwavable package of claim 23, wherein the respective rims of thefirst cup and the second cup are joined separably by a removable plastictear-tape on at least a portion of the exterior surface of the package.30. The microwavable package of claim 23, wherein the first cup isjoined to the second cup using a plastic shrink-wrap.
 31. Themicrowavable package of claim 23, wherein at least one of the first cupand the second cup includes a flattened end distal the rim thereof. 32.The microwavable package of claim 23, wherein the first cup and thesecond cup are arranged in an upright configuration such that one of thefirst cup and the second cup serves as a bottom cup, and the bottom cupcomprises a flattened end distal the rim thereof.
 33. The microwavablepackage of claim 23, wherein at least one of the first cup and thesecond cup includes a vent window.
 34. The microwavable package of claim23, wherein the microwave energy interactive material comprises asusceptor.
 35. The microwavable package of claim 23, wherein at least aportion of only one of the first cup and the second comprises themicrowave energy interactive material.
 36. The microwavable package ofclaim 23, wherein at least a portion of both first cup and the secondcup independently comprises the microwave energy interactive material.37. The microwavable package of claim 23, wherein at least a portion ofthe exterior surface of the package comprises an insulating material.38. The microwavable package of claim 23, wherein at least a portion ofthe interior surface of at least one of the first cup and the second cupis corrugated, and at least a portion of the microwave energy activematerial is deposited on the corrugated surface.
 39. The microwavablepackage of claim 23, wherein the first cup and the second cup eachindependently comprise an end distal the major opening, and the firstcup and the second cup are capable of being stacked in a nestedconfiguration with the respective major openings adjacent to one anotherand the respective ends being adjacent one another.
 40. A microwavablepackage for heating a food item, the package comprising: a first portionadapted to receive a food item, the first portion having an interiorsurface at least partially comprising a microwave energy interactivematerial; a second portion dimensioned to be gripped by a user; and awall separating the first portion and the second portion.
 41. Themicrowavable package of claim 40, wherein at least one of the firstportion and the second portion includes a venting feature.
 42. Themicrowavable package of claim 40, wherein the first portion comprises aremovable sheet for accessing a food item therein.
 43. The microwavablepackage of claim 40, wherein the first portion and the second portionare arranged in an upright configuration, such that the first portion isan upper portion, the second portion is a lower portion, and the wallseparating the first portion and the second portion serves as a floor ofthe upper portion.
 44. The microwavable package of claim 40, wherein thelower portion is tapered from the upper portion towards a bottom end ofthe lower portion.
 45. The microwavable package of claim 40, wherein thebottom end of the lower portion is flattened.
 46. A microwave packagecomprising: a carton form including a base with a central fold line, afirst side wall foldably joined to the base along a first fold line, anda second side wall foldably joined to the base along a second fold line;and a pouch disposed between the base, the first side wall, and thesecond side wall of the carton form, the pouch comprising a microwaveenergy interactive material.
 47. The package of claim 46, wherein thecarton form and the pouch may be transformed from a first, flattenedconfiguration to a second, erected configuration with the first sidewall and the second side wall being maintained in tension by the base.48. The package of claim 46, wherein the first fold line and the secondfold line are convexly curved, and in the second configuration, the baseof the carton form assumes a, concavely curved form with the first sidewall and the second side wall of the carton form being bowed or convexlycurved.
 49. The package of claim 46, wherein the pouch is affixed to atleast one of the first side wall and the second side wall of the cartonform.
 50. The package of claim 46, wherein the microwave energyinteractive material comprises a layer of metal sufficiently thin toconvert at least a portion of impinging microwave energy into thermalenergy.
 51. The package of claim 46, wherein the microwave energyinteractive material comprises a layer of metal, the layer of metal issupported on a first polymer film, a dimensionally stable substrate isjoined to the layer of metal, and a second polymer film is joined to thedimensionally stable substrate in a patterned configuration, therebydefining a plurality of closed cells between the second polymer film andthe dimensionally stable substrate, wherein at least some of the closedcells inflate in response to microwave energy.
 52. The carton of claim51, wherein when the closed cells inflate in response to microwaveenergy, the first polymer film, the layer of microwave energyinteractive material, and the dimensionally stable substrate bulge awayfrom the second polymer film.
 53. The carton of claim 51, wherein whenthe closed cells inflate in response to microwave energy, the secondpolymer film bulges away from the first polymer film, the layer ofmicrowave energy interactive material, and the dimensionally stablesubstrate.
 54. A package for heating a food item in a microwave oven andcomfortable handling thereafter, the package comprising: a flexiblepouch at least partially formed from a microwave energy interactivematerial, wherein the microwave energy interactive material increases intemperature in response to being exposed to microwave energy; and adimensionally stable carton at least partially joined to and receivingat least a portion of the sleeve, the carton including at least one areathat is substantially transparent to microwave energy, wherein thetransparent area remains substantially cool to the touch in response tobeing exposed to microwave energy.
 55. The package of claim 54, whereinthe microwave energy interactive material is supported on a polymerfilm.
 56. The package of claim 54, wherein the pouch comprises aninsulating microwave packaging material including a plurality of closedcells that expand in response to exposure to microwave energy, and theinsulating microwave packaging material includes the microwave energyinteractive material.
 57. The package of claim 56, wherein theinsulating microwave packaging material includes a susceptor comprisingthe microwave energy interactive material supported on a first polymerfilm layer, a moisture-containing layer joined to the microwave energyinteractive material, and a second polymer film layer joined to themoisture-containing layer in a predetermined pattern, thereby forming atleast one closed cell between the moisture-containing layer and thesecond polymer film layer.
 58. The package of claim 56, wherein theinsulating microwave packaging material includes the microwave energyinteractive material supported on a first substantially vaporimpermeable substrate, a dimensionally stable substrate bonded to themicrowave energy interactive material, and a second substantially vaporimpermeable substrate bonded to the dimensionally stable substrate alongbond lines formed in a pattern, wherein the bond lines are substantiallyvapor impermeable, and the pattern defines a plurality of closed cellsbounded by the second substantially vapor impermeable substrate, thedimensionally stable substrate, and the bond lines, wherein uponimpingement of the insulating microwave packaging material by microwaveenergy in a microwave oven, each of the plurality of closed cellsexpands to form an insulating pocket.
 59. The package of claim 58,wherein the insulating pocket comprises a bulging side and an opposingside, the bulging side comprises a portion of each of the firstsubstantially vapor impermeable substrate, the microwave energyinteractive material, and the dimensionally stable substrate, theopposing side comprises a portion of the second substantially vaporimpermeable substrate, and the bulging side lofts away from the opposingside.
 60. The package of claim 58, wherein the insulating pocketcomprises a bulging side and an opposing side, the bulging sidecomprises a portion of the second substantially vapor impermeablesubstrate, the opposing side comprises a portion of each of the firstsubstantially vapor impermeable substrate, the microwave energyinteractive material, and the dimensionally stable substrate, and thebulging side lofts away from the opposing side.
 61. A microwave energyinteractive insulating material comprising: a layer of microwave energyinteractive material supported on a first polymer film; a dimensionallystable substrate joined to the layer of microwave energy interactivematerial; and a second polymer film joined to the dimensionally stablesubstrate in a patterned configuration that defines a plurality ofclosed cells between the dimensionally stable substrate and the secondpolymer film, wherein upon sufficient exposure to microwave energy, atleast some of the closed cells inflate, and the first polymer film, thelayer of microwave energy interactive material, and the dimensionallystable substrate bulge away from the second polymer film.
 62. Theinsulating material of claim 61, further comprising a paper layer joinedto the first polymer film on a side of the first polymer film oppositethe microwave energy interactive material.
 63. The insulating materialof claim 61, wherein the inflated cells are adapted to provide thermalinsulation for at least one of a food item adjacent to the insulatingmaterial, and the layer of microwave interactive material.
 64. Theinsulating material of claim 61, wherein the first polymer film and thesecond polymer film are each substantially vapor impermeable.
 65. Theinsulating material of claim 61, wherein upon impingement of theinsulating material by microwave energy, the microwave energyinteractive layer generates sensible heat that heats and softens thefirst polymer film.
 66. The insulating material of claim 65, whereinupon impingement of the insulating material by microwave energy, thesensible heat further heats the second polymer film, and the secondpolymer film contracts in at least one of an X direction and a Ydirection.
 67. The insulating material of claim 61, wherein when thefirst polymer film, the layer of microwave energy interactive material,and the dimensionally stable substrate bulge away from the secondpolymer film, the second polymer film remains substantially flat. 68.The insulating material of claim 61, wherein upon impingement of theinsulating material by microwave energy, a distance between the secondpolymer film and the dimensionally stable substrate in a center of atleast one of the plurality of closed cells increases by at least anorder of magnitude more than the distance before impingement bymicrowave energy.
 69. The insulating material of claim 61, wherein uponimpingement of the insulating material by microwave energy, a distancebetween the second polymer film and the dimensionally stable substratein a center of at least one of the plurality of closed cells increasesby up to 30 times more than the distance before impingement by microwaveenergy.
 70. The insulating material of claim 61, wherein the microwaveenergy interactive material comprises aluminum, the dimensionally stablesubstrate comprises paper, paperboard, or any combination thereof, andthe second polymer film comprises biaxially-oriented polyester.
 71. Theinsulating material of claim 61, wherein the first polymer film and thesecond polymer film are each substantially vapor impermeable, the secondpolymer film is joined to the dimensionally stable substrate with anadhesive in a patterned configuration, and the adhesive penetrates thedimensionally stable substrate to form a substantially vapor impermeablebarrier in conjunction with the first polymer film and the secondpolymer film.
 72. The insulating material of claim 71, wherein themicrowave energy interactive material is inactivated in a patterncorresponding to the patterned configuration of the adhesive.
 73. Theinsulating material of claim 61, wherein the closed cells have a shapeselected from the group consisting of a circle, an oval, a curvilinearshape, a symmetrical curvilinear shape, a triangle, a square, arectangle, a polygon, a right polygon, and an equilateral polygon. 74.The insulating material of claim 61, wherein the closed cells aresubstantially square in shape, substantially hexagonal in shape, or anycombination thereof.
 75. The insulating material of claim 61, whereinthe closed cells are substantially elongate in shape.
 76. A microwavepackaging material comprising: a susceptor film comprising a microwaveenergy interactive material supported on a first polymer film layer; amoisture-containing layer joined to the microwave energy interactivematerial; and a patterned adhesive layer joining a second polymer filmto the moisture-containing layer, thereby defining at least one, closedcell between the moisture-containing layer and the second polymer filmlayer.
 77. The microwave packaging material of claim 76, wherein thefirst polymer film layer comprises a biaxially-oriented polyester, themoisture-containing layer comprises a paper, and the second polymer filmlayer comprises a biaxially-oriented polyester.
 78. The microwavepackaging material of claim 76, wherein the closed cell expands when themicrowave packaging material is exposed to microwave energy.
 79. Themicrowave packaging material of claim 76, wherein themoisture-containing layer releases water vapor when the microwavepackaging material is exposed to microwave energy.
 80. The microwavepackaging material of claim 76, wherein upon exposure to microwaveenergy, the moisture-containing layer releases water vapor, therebyinflating the closed cell.
 81. A microwave packaging material consistingessentially of: a first polymer film layer; a microwave energyinteractive material layer supported on the first polymer film; amoisture-containing layer joined to the microwave energy interactivematerial layer; a second polymer film layer; and a patterned adhesivelayer disposed between and joining the moisture-containing layer and thesecond polymer film layer, wherein the patterned adhesive layer definesa plurality of closed cells between the moisture-containing layer andthe second polymer film.
 82. The microwave packaging material of claim81, wherein the moisture-containing layer releases water vapor when themicrowave packaging material is exposed to microwave energy, therebyinflating at least some of the plurality of closed cells.
 83. Amicrowave energy interactive structure comprising: a first sheet and asecond sheet of microwave energy interactive insulating materialadjoined in a superposed, contacting relationship, wherein the microwaveenergy interactive insulating material includes a layer of microwaveenergy interactive material supported on a first polymer film; adimensionally stable substrate joined to the layer of microwave energyinteractive material; and a second polymer film joined to thedimensionally stable substrate in a patterned configuration that definesa plurality of closed cells between the dimensionally stable substrateand the second polymer film, wherein at least some of the closed cellsinflate upon sufficient exposure to microwave energy.
 84. The structureof claim 83, wherein when the closed cells inflate, the first polymerfilm, the layer of microwave energy interactive material, and thedimensionally stable substrate bulge away from the second polymer film.85. The structure of claim 84, wherein when the closed cells inflate,the second polymer film remains substantially flat.
 86. The structure ofclaim 84, wherein when the closed cells inflate, the second polymercontracts in at least one of an X direction and a Y direction, the Xdirection being substantially perpendicular to the Y direction.
 87. Thestructure of claim 84, wherein the second polymer film comprisesbiaxially oriented polyester.
 88. The structure of claim 83, whereinwhen the closed cells inflate, the second polymer film bulges away fromthe first polymer film, the layer of microwave energy interactivematerial, and the dimensionally stable substrate.
 89. The structure ofclaim 88, wherein when the closed cells inflate, the first polymer filmremains substantially flat.
 90. The structure of claim 88, wherein thesecond polymer film comprises amorphous polyester.
 91. The structure ofclaim 83, wherein the first sheet and the second sheet are joined suchthat the second polymer film of the first sheet is in a contactingrelationship with the first polymer film of the second sheet.
 92. Thestructure of claim 83, wherein the first sheet and the second sheet arejoined such that the second polymer film of the first sheet is in acontacting relationship with the second polymer film of the secondsheet.
 93. The structure of claim 83, wherein the first sheet and thesecond sheet are joined such that the first polymer film of the firstsheet is in a contacting relationship with the first polymer film of thesecond sheet.
 94. The structure of claim 83, wherein the first sheet andthe second sheet are joined along a plurality of points proximate aperimeter of each the first sheet and the second sheet.
 95. Thestructure of claim 83, wherein the first sheet and the second sheet arejoined substantially continuously to one another.
 96. The structure ofclaim 95, wherein the first sheet and the second sheet are joinedsubstantially continuously to one another using a substantiallycontinuous layer of adhesive.
 97. A microwave energy interactiveinsulating package comprising a plurality of adjoined panels that definea cavity for receiving a food item, wherein at least one panel of theplurality of adjoined panels comprises an microwave energy interactiveinsulating material including a layer of microwave energy interactivematerial supported on a first polymer film, a dimensionally stablesubstrate joined to the layer of microwave energy interactive material,and a second polymer film joined to the dimensionally stable substratein a patterned configuration that defines a plurality of closed cellsbetween the dimensionally stable substrate and the second polymer film,and wherein upon sufficient exposure to microwave energy, at least someof the closed cells inflate, and the first polymer film, the layer ofmicrowave energy interactive material, and the dimensionally stablesubstrate bulge toward the cavity.
 98. The package of claim 97, furthercomprising an interior surface at least partially defined by the firstpolymer film.
 99. The package of claim 97, wherein the plurality ofadjoined panels includes a first panel and a second panel in an opposed,facing relationship with the cavity therebetween.
 100. The package ofclaim 99, wherein the first panel and the second panel each comprise theinsulating material, and the package further comprises an interiorsurface at least partially defined by the first polymer layer of thefirst panel and the first polymer layer of the second panel.
 101. Thepackage of claim 99, further comprising a third panel joined to thesecond panel in a facing relationship, wherein the third panel comprisesthe microwave energy interactive insulating material.
 102. Amicrowavable food carton comprising: an interior surface; and a sheet ofmicrowave energy interactive insulating material joined to at least aportion of the interior surface, wherein the microwave energyinteractive insulating material includes a layer of microwave energyinteractive material supported on a first polymer film, a dimensionallystable substrate joined to the layer of microwave energy interactivematerial, and a second polymer film joined to the dimensionally stablesubstrate in a patterned configuration that defines a plurality ofclosed cells between the dimensionally stable substrate and the secondpolymer film, wherein at least some of the closed cells inflate inresponse to microwave energy.
 103. The carton of claim 102, wherein whenthe closed cells inflate in response to microwave energy, the firstpolymer film, the layer of microwave energy interactive material, andthe dimensionally stable substrate bulge away from the second polymerfilm.
 104. The carton of claim 102, wherein when the closed cellsinflate in response to microwave energy, the second polymer film bulgesaway from the first polymer film, the layer of microwave energyinteractive material, and the dimensionally stable substrate.
 105. Thecarton of claim 102, wherein the sheet includes a perimeter, and thesheet includes at least one slit adjacent to the perimeter, the slitbeing adapted to allow the sheet to expand or contract in response tomicrowave energy.
 106. A microwave energy interactive insulatingmaterial comprising: a layer of microwave energy interactive materialsupported on a first polymer film; a dimensionally stable substratejoined to the layer of microwave energy interactive material; and asecond polymer film joined to the dimensionally stable substrate in apatterned configuration that defines a plurality of closed cells betweenthe dimensionally stable substrate and the second polymer film, whereinupon sufficient exposure to microwave energy, at least some of theclosed cells inflate, and the second polymer film bulges away from thedimensionally stable substrate, the layer of microwave energyinteractive material, and the first polymer film.
 107. The insulatingmaterial of claim 106, further comprising a paper layer joined to thefirst polymer film on a side of the first polymer film opposite themicrowave energy interactive material.
 108. The insulating material ofclaim 106, wherein the first polymer film and the second polymer filmare each substantially vapor impermeable.
 109. The insulating materialof claim 106, wherein the second polymer film is joined to thedimensionally stable substrate in a patterned configuration byselectively heating a portion the second polymer film in the patternedconfiguration.
 110. The insulating material of claim 106, wherein theportion of the second polymer film that is selectively heated penetratesthe dimensionally stable substrate to form a substantially vaporimpermeable barrier in conjunction with the first polymer film and thesecond polymer film.
 111. The insulating material of claim 106, whereinupon impingement of the microwave energy interactive material bymicrowave energy, the microwave energy interactive layer generatessensible heat that heats and softens the second polymer film.
 112. Theinsulating material of claim 106, wherein when the closed cells inflate,the softened second polymer film bulges away from the first polymerfilm, and the first polymer film remains substantially flat.
 113. Theinsulating material of claim 106, wherein upon impingement of theinsulating material by microwave energy, a distance between the secondpolymer film and the dimensionally stable substrate in a center of atleast one of the plurality of closed cells increases by at least anorder of magnitude more than the distance before such impingement. 114.The insulating material of claim 106, wherein upon impingement of theinsulating material by microwave energy, a distance between the secondpolymer film and the dimensionally stable substrate in a center of atleast one of the plurality of closed cells increases by up to 30 timesmore than the distance before such impingement.
 115. The insulatingmaterial of claim 106, wherein the inflated cells reduce heat loss fromat least one of a food item adjacent to the insulating material, and thelayer of microwave interactive material.
 116. The insulating material ofclaim 106, wherein the dimensionally stable substrate comprises a paper,paperboard, or any combination thereof, and the second polymer filmcomprises amorphous polyester.
 117. A microwave energy interactivepackage comprising an outer surface at least covered by a microwaveenergy interactive insulating material including: a layer of microwaveenergy interactive material supported on a first polymer film; adimensionally stable substrate joined to the layer of microwave energyinteractive material; and a second polymer film joined to thedimensionally stable substrate in a patterned configuration that definesa plurality of closed cells between the dimensionally stable substrateand the second polymer film, wherein upon sufficient exposure tomicrowave energy, at least some of the closed cells inflate, and thesecond polymer film bulges away from the dimensionally stable substrate,the layer of microwave energy interactive material, and the firstpolymer film.
 118. The package of claim 117, comprising an outer surfaceat least partially defined by the second polymer film.
 119. The packageof claim 118, wherein when the closed cells inflate, the outer surfaceremains cool to the touch.
 120. The package of claim 117, comprising aplurality of adjoined panels, at least one panel including an exteriorsurface at least partially defined by the second polymer film.
 121. Thepackage of claim 120, wherein the closed cells inflate, the outersurface remains cool to the touch.
 122. The package of claim 117,wherein the second polymer film is joined to the dimensionally stablesubstrate in a patterned configuration by selectively heating a portionthe second polymer film in the patterned configuration.
 123. The packageof claim 117, wherein the portion of the second polymer film that isselectively heated penetrates the dimensionally stable substrate to forma substantially vapor impermeable barrier in conjunction with the firstpolymer film and the second polymer film.
 124. The package of claim 117,wherein upon impingement of the microwave energy interactive material bymicrowave energy, the microwave energy interactive layer generatessensible heat that heats and softens the second polymer film.
 125. Theinsulating material of claim 117, wherein when the closed cells inflate,the softened second polymer film bulges away from the first polymerfilm, and the first polymer film remains substantially flat.
 126. Theinsulating material of claim 117, wherein the dimensionally stablesubstrate comprises a paper, paperboard, or any combination thereof, andthe second polymer film comprises amorphous polyester.
 127. A packagefor heating a food item in a microwave oven and comfortable handlingthereafter, the package comprising: an insulating microwave packagingmaterial including a plurality of expandable closed cells, theinsulating microwave packaging material including at least one area thatis microwave energy active and at least one area that is microwaveenergy inactivated, wherein the microwave energy active area increasesin temperature upon exposure to microwave energy, and wherein themicrowave energy inactivated area remains substantially cool to thetouch upon exposure to microwave energy.
 128. The package of claim 127,wherein the insulating microwave packaging material includes a susceptorfilm comprising a microwave energy interactive material supported on afirst polymeric film layer, wherein the microwave energy interactivematerial is inactivated in the microwave energy inactivated area, amoisture-containing layer superposed with the microwave energyinteractive material, and a second polymeric film layer joined to themoisture-containing layer in a predetermined pattern, thereby forming atleast one closed cell of the expandable cells between themoisture-containing layer and the second polymeric film layer.
 129. Thepackage of claim 127, wherein the insulating microwave packagingmaterial includes a first substantially vapor impermeable substrate, alayer of microwave energy interactive material supported by the firstsubstantially vapor impermeable substrate, wherein the microwave energyinteractive material is inactivated in the microwave energy inactivatedarea, a dimensionally stable substrate bonded to the layer of microwaveinteractive material, and a second substantially vapor impermeablesubstrate bonded to the dimensionally stable substrate along bond linesformed in a pattern, wherein the bond lines are substantially vaporimpermeable, and the pattern defines a plurality of closed cells boundedby the second substantially vapor impermeable substrate, thedimensionally stable substrate, and the bond lines, wherein uponimpingement of the insulating microwave packaging material by microwaveenergy in a microwave oven, each of the plurality of closed cellsexpands to form an insulating pocket.
 130. The package of claim 129,wherein the insulating pocket includes a bulging side and an opposingside, the bulging side comprises a portion of each of the firstsubstantially vapor impermeable substrate, the microwave energyinteractive material layer, and the dimensionally stable substrate, theopposing side comprises a portion of the second substantially vaporimpermeable substrate, and the bulging side lofts away from the opposingside.
 131. The package of claim 129, wherein the insulating pocketcomprises a bulging side and an opposing side, the bulging sidecomprises a portion of the second substantially vapor impermeablesubstrate, the opposing side comprises a portion of each of the firstsubstantially vapor impermeable substrate, the microwave energyinteractive material layer, and the dimensionally stable substrate, andthe bulging side lofts away from the opposing side.